Firstly studies (to which I can link you if you like) show that children are born with an instinctual belief in unseen agency.
They assume that things which happen are purposely directed by intelligence.
Further, they operate off the assumption that everything has some kind of purpose or design. In fact, when pressed to give quick decisions or answers, even naturalist scientists default to the instinct of purpose and design.
Another study shows that there is a universal belief across cultures throughout the world in both some kind of divine force and in mind/body duality. This could be easily demonstrated by trying to find anybody anywhere who doesn’t know what you are talking about when you talk about God.
Consider this: how difficult is it to communicate the concept of prayer to a child? Turns out, not very difficult at all. Now try EXPLAINING the concept of prayer as a dictionary definition. It actually isn’t easy to provide a definition of exactly what prayer means, at least not without assuming the concept of God as a given.
Two more psychological phenomena are instrumental in demonstrating this knowledge of God. One comes in the form of the recognized stages of grief. One of the stages is “bargaining.” Essentially, when someone is going through grief, they start trying to bargain with an unseen and powerful intelligence – again, instinctually, whether or not they are religious.
Finally, there is the concept of gratitude. When one experiences something positive, they also experience a sense of gratitude. Now gratitude is inherently directional and personal. You can’t just throw gratitude off into nothingness. You have to be grateful TO SOMEONE. I have personally witnessed this where an atheist expresses gratitude to “the universe,” because they don’t have any larger personal force to which their worldview allows them to express their gratitude. There are more arguments I could make, but based on these alone, I think it’s safe to say that people have an inherent knowledge of God.