Evidence??

[robvalue]

I'd say please define what you mean by "God", and in what sense does it "exist". Then I would ask to see the evidence, to see if it backed up the claim, assuming the claim was testable. If the claim is untestable, or incoherent, then they need to come up with a new claim.

I can't answer what is evidence for "God existing" because both of those words have such a huge scope for interpretation.

But any evidence that would convince me beyond reasonable doubt of its existence. As has been seen in my God claim topic, no one has even made a testable claim yet, even a hypothetical one. That's the first hurdle.