You've omitted part of the question, which should read "If God exists and interacts/affects the world, where would we get the evidence?"
And that's simple, any such interaction/effect would leave a trace, and that trace would be evidence.
I believe that the evidence is the Messengers that God sends and what they leave in their wake, including the great civilizations they are responsible for.
RELIGION AND CIVILIZATION
Okay then, what is the evidence? You claim that it is in the existence of "Messengers of God." But how do you know who they are, when there have been so very many claimants? Most of the religions of the world exist because they have each accepted some -- but not other -- such claimants.
I made a list of the minimum criteria that a Messenger of God would mage to meet.
The minimum criteria would be:
1. He had good character as exemplified by his qualities such as love, mercy, kindness, truth, justice, benevolence, gracious, merciful, righteous, forgiving, patient.
2. He believed he had been given a mission by God and did everything he could to see that it was carried out. He was completely successful before his death, and he accomplished everything that he set out to do.
3. He wrote much about God and God's purpose for humans both individually and collectively, or scriptures were written by others who spoke for him. He firmly believed that the work he was doing was for the Cause of God.
4. He had many followers while he was alive, and there are still millions who follow his teachings and gather in groups based on the religion he founded.
5. His followers have grown more numerous in recent times.
This is a starting point but there are other questions we would want to ask ourselves before we would be able to believe that a man was a true Messenger of God because that is a bold claim so there should be a lot of evidence to support such a claim.
Other criteria he would have to meet is that his religion could not contradict or be in opposition to any of the world religions that are already established and he could not talk down any of those religions and say his religion is the only true religion from God. That would be a dead giveaway that he was trying to promote his religion as being the only true one, which would lead to suspicion right off the bat because none of the true Messengers of God have talked down other Messengers who preceded them. It is the followers of these religions that talk down the other religions, not the Messengers. There are reasons for that but I do not want to get off the subject at hand.