Forgive me in advance because I'm going to take a little bit to get to the point here. In order to get there I think I need to address 3 questions:
1. Defining "truth" and understanding some of the various theories of truth
2. Discussing the relation between truth and knowledge ("what is true?" in relation to "how do we know?")
3. Addressing the foundations of logical reasoning and the transcendental argument for God (the claim that God is a precondition for knowledge is the transcendental argument)
1. Defining truth
So, as you might guess, the word has been given a number of definitions and uses which are all kind of related but distinct. I'm going to suggest that the most intuitive theory of the nature of truth, and the one generally assumed by your interlocutor, is called the "correspondence theory" of truth, which deals with the truth of propositions, where a proposition P is a sentence like "the sky is blue". In the correspondence theory of truth we might say:
A proposition P is true if and only if the state of affairs described by P exists in reality
That is, the truth of P depends on the correspondence between P and the world.
2. Truth and Knowledge
In and of itself, correspondence theory is silent about epistemology, i.e the question "how do we know the truth?" It draws a distinction between "true" and "known", and while that distinction is useful, in practice of course the question of truth is tightly connected to the question of knowledge. This tension between the two polls also exists in epistemology, where the classical definition of "knowledge" is "justified, true, belief". But just as with the correspondence theory, the pressing issue is that justification really is everything, since apart from a justification we have no means of deciding whether the belief is "true" or not.
In modern usage, when we're using a correspondence theory of truth we are generally also using an epistemology that emphasizes empirical evidence, as in science, because the history of science and philosophy has demonstrated that scientific/empiric methodology is the most appropriate for attaining knowledge about the world.
One of the primary distinctions between correspondence theory and other theories of truth is that most of the others take into account epistemological concerns directly. That is, coherence theory says that the criterion of truth is the coherence of P with the set of other true propositions. The objection of course is that some set of beliefs might be coherent but completely disconnected from reality, but the value of coherence theory is that coherence is really an epistemological justification. We are more justified to believe that P if P is coherent with other things we know. Other theories take into account that we would like to use the word "true" to describe things that aren't easy to reduce to questions about the physical world which can be given decisive scientific answers. Social construction theories of truth for example deal with the kinds of knowledge that arises relative to particular cultures and societies, where the body of knowledge is not really about the objective physical world. Pluralism with regard to truth recognizes that we may need different epistemologies and different criteria for truth in different contexts.
In any case, this is a bit of a sideline, but I think it's useful to understand how truth and knowledge are tightly connected. Mainly, the question put to you was concerned with correspondence theory.
2a. "Truth" as a transcendental
One final note before (3). I've been using "true" as a word that describes a property of some particular proposition P. The other word we encounter is "Truth" with a capital-T, which is supposed to represent the kind of overarching unity of truth. "Truth" is somehow more than just the collection of truths. This idea owns in large part to certain foundational laws of classical logic which I'll address in (3). Essentially, the law of non-contradiction seems to require that all truths be compatible, as with the coherence theory of truth. Because A and not-A can't both be true. This intuition about truth becomes important to the transcendental argument for God that was put to you.
3. Foundations of Logic and the TAG
"God is a precondition of knowledge" is an argument of presuppositional apologetics, sometimes called the transcendental argument for God. I believe the first version of it owes to Immanuel Kant. In order to understand the argument we have to talk about the foundational rules of classical logic. There is more than one formulation of classical logic but I'll just deal with the most common ones, which go back to Aristotle more or less:
1. The law of identity (A=A)
2. The law of non-contradiction (not (A and not-A) -- A and not-A can't both be true)
3. The law of the excluded middle (a proposition is either true or false, there is no middle ground)
We call them first principles of logic precisely because they are taken as assumptions, as principles which are self-evidently true. Or, if we're being more cautious, we simply say that we assume them because we can't get anywhere with classical logic without assuming them, and we can't figure out how to derive them from any more fundamental principles. The important part, from the perspective of TAG, is precisely that they are
presuppositions, i.e things we hold to be true despite a lack of demonstration within the logical systems we build on top of them.
The transcendental argument, then, asserts that in assuming the truth of the foundational laws, we already implicitly assume the existence of God. The argument hinges on the concept of God as a kind of ultimate ground of everything. It's similar in that way to the cosmological argument I referenced before. The cosmological argument recognizes a possible infinite regression of causes if everything in reality requires a cause, and declares the sui generis uncaused first cause to be God. The transcendental argument recognizes a possible infinite regression of justification in logic and epistemology, and declares the un-justified sui generis laws of logic to depend on that same God.
Another way of expressing the transcendental argument is more abductive. We recognize that the reason logical reasoning is useful is because for some reason the world has a kind of logical structure. It is intelligible in this way, and demonstrates patterns that are amenable to our thinking. The transcendental argument asserts that without God we have no reason to believe that we should have expected the world to be like that.
The problem with TAG
As I said in my first response, I think the main issue is that the "God" of the transcendental argument is basically content-less. It just gives a name to a kind of property that is supposed to be necessary (the property of being the terminus of an otherwise infinite regress) but that property, even if we agree it must exist, doesn't imply any other property that is usually attributed to God. In the case of the cosmological argument, we might accept that the principle of sufficient reason (everything must have a cause) breaks down, and that there must be some existence which is just a brute fact, or is self-existent, but we have no reason to call that thing "God" rather than just "universe". The same applies to the TAG.
In fact, as an abductive argument the opposite of TAG might be stronger than TAG. The success scientific methodology in understanding the world, including the intelligibility and ordered-ness of the world would rather seem to imply that it's unlikely that the world was created by an omnipotent and anthropomorphic will, which, considering human will, we might expect would have led to a much less "logical" reality than the one we find. Beyond that, there is of course the fact that nowhere does the logic or methodology of science require any consideration of a deity or of the value of sacred texts or traditions. It's probably worth noting that many classical theologies end up de-anthropomorphizing their conceptions of God for reasons related to the first, but as a whole the intelligible order of the natural world would seem to do more to call into question traditional religious dogmas than to confirm them.
What is true? How do we know?
Going back to the discussion about truth and knowledge, I tend to think the pluralist critique of the idea of a single, overarching and absolute truth is reasonable. Because truth and knowledge are so intricately connected, the idea of an absolute and objective truth entirely disconnected from "how do we know?" isn't useful at all. It's an abstraction that can't really exist, at least for us, because we have no access to it. We might reject this idea of truth as excessively metaphysical in the same way Buddhism is skeptical of metaphysics. The idea of absolute certainty about knowledge is likewise less than useful.
In practice, the "how?" is more important, and the best way we've found to arrive at truth is also the best way to make our knowledge more reliable. That is, by intelligently applying criteria that are relevant to the kind of question we are asking, by being humble and aware of our own limitations and cognitive biases, by being self-critical and skeptical, and by looking for objective and repeatable ways of testing hypotheses where those tests are possible.