This is unknowable by human knowledge.
God by definition is:
- Omnipotent (all-powerful)
- Omniscient (all-knowing)
...actually, omnipotence implies omniscience. One cannot be all-powerful if one lacks the knowledge to commit certain powers. To know god, one needs to know omniscience. To know omniscience, one needs to be omniscient. If one is omniscient, one is god. You're not that smart. If god truly cares if I believe in him, he'd tell me. He's got the power and knows I don't know whether he exists.
Some also add:
- Infinite (everything)
- Omnipresent (everywhere)
- Eternal (ever-lasting)
- Creator (ultimate creator of everything)
...but these terms really don't mean anything and imply paradoxes. To say god is everywhere or everything is to say that everything is everything or A=A. Circular logic. Nothing new is learned here. God as creator of all implies infinite reduction paradox. If everything is created by god, what created god? If the universe is only composed of matter, how does god create something (matter) out of nothing? How is god a creator, separate from its creation, and part of it at the same time? Meaningless.
Still others add:
- Omnibenevolent (all-good)
- Perfect (lacking nothing)
...but these are subjective terms and anything subjective is unreal.
God as sub-creator (of this particular universe or parts thereof).
Since this god is only a sub-creator (itself being created and thus not the ultimate god), it is possibly but not necessarily knowable. It is also not necessarily benign and thus to "know god" may not necessarily be a fruitful venture. Note that humans are also sub-creators, thus gods by this definition. So are ants and amoeba. So is anything that "creates" anything else. Actually, since to create means to cause to exist or bring into being, anything that causes something else to happen creates it and that's everything in known reality (from sub-atomic particles to the macrocosm of the universe). Again even this definition of god is utterly meaningless.
So if it is impossible to know if the ultimate god exists, which religion is correct?
The first 4 pics above are part of the same Triptych piece by Hieronymous Bosch, The Garden of Earthly Delights. The outer panel (creation) unfolds to reveal the Garden of Eden (left panel), Earth (center panel), Hell (right panel). The head of my philosophy dept. was the one person I knew to have a replica of the fully-opening piece.