Is there finally an argument for the existence of God?

No. @Calilasseia’s right. The very definition of atheism is rejection of current (and past, I guess) claims to deity and if you know nothing else about a person than them being an atheist there’s nothing else you can determine about them.

To give a simple example (a question), Nik is an atheist what can you tell me about this person?

UK Atheist