The distinction is not as great as you are making it out to be. Knowledge is about degree of certainty regarding the truth of a claim, but claims can only have truth if they can be understood. Otherwise, they are simply anomalous propositions dressed up as claims.
And it IS understood.
We can drop the metaphor if you like. I was being cute about it, and I didn't mean to be disrespectful. I'm ok with ending the argument is disagreement, if that's how it must be. The fact remains that you literally do not know what you are talking about if you are talking about something that is unknowable. That has to do with what the word "unknowable" means. My position is that knowability entails understanding, because the very process of understanding a proposition requires one to understand the conditions under which it could be true, false, or simply incoherent. Incoherence happens when you construct a claim based on false presuppositions.
Let's start from the end, and work backwards. Incoherence is not a claim based on false presuppostions. If the presuppositions are proven false then the proposition is invalid. Incoherence means the individual ideas do not stick/adhere to each other or to the conclusion that is being attempted.
When I say "If God is understood to be infinite, then God is unknowable." That's not incoherent.
Understanding does include the things you mentioned, but it does not require knowledge. Understanding is able to derive knowledge as needed. It knows where to look. It knows how to research. It is also able to evaluate relevance ( which evaluates coherence ). And it is also able to locate counter-examples and contradictions ( evaluates rigor ).
Knowledge is able to evaluate true / false, but it's ignorant of what it doesn't know. It doesn't make connections. It's just facts, and it has no method for testing those facts. It will never realize one of those facts is erroneous until it stumbles on updated information.
Sure, knowability entails understanding. But lack of knowability does not entail lack of understanding. The negation of "knowability entails understanding" is "lack of understanding entails lack of knowability". And that negation is false. I know your screen-name. But I don't understand why you chose it.
So, there is not a bijunctive relationship between knowledge and understanding. They're very different intellectual phenomena. What's understood is that "knowing" is irrelevant to an infinite being, because infinite means it is never-ending, and the knowing will never complete.
If the question is: How do you know that God is infinite? The answer is "I don't know." And that is consistent with my original claim. Because infinity, itself, is not known. It has no borders or boundries.
But what assumptions are hidden in your declaration that this putative being is "infinite"? We do in fact understand the meaning of infinity and can define it easily in logical or mathematical terms. The original idea applies to quantifiability--counting and repetitiveness. Your usage seems more metaphorical than literal, since the quantifiable properties of God are left unstated and obscure. That's what makes your god "unknowable"--the convenient use of unstated and therefore unverifiable properties. It is basically just handwaving when you lack an ability to justify your claim.
I only declared that this is the proper defintion of God.
Regarding infinity, the model you are using is limited, apparently to a single dimension. Keep going... dot to infinite line, infinite line to infinite plane, infinite plane to infinite cube, infinite cube to infinite versions of the cube... 5 dimensions, 6 dimensions, 7 dimensions. The best description I can come up with is an infinite database where infinite objects are connected in many-to-many-relationships with each other. That would be literal infinity. Not metaphor. Literal.
However, when it comes to justification... well... that's different.
First question... imo... always-always: Is it harmful?
Is there any potential harm in defining God this way?
Next question:
Is there any contradiction in what I said?
Next question:
Is anything I said proven false?
Next question:
Does the conclusion describe real-world phenomena?
It seems like you are focused on what appears to be a contradiction. But I disagree. It's a special case where something can be understood to be unknowable. There isn't a contradiction, it's simply a harmless supposition that cannot be proven false, and has explanatory power.