The demand for proof of God’s existence is sometimes a trick. It may be a reasonable request for evidence, but often it is not. Unless you know in advance what kind of evidence would count (scientific? historical? philosophical arguments? revelation?) or what kind of “proof” would be satisfying (absolute proof? proof beyond a reasonable doubt? proof based on the preponderance of evidence?), you’ll probably be wasting your time. It’s too easy for an intellectually dishonest person to dismiss your efforts. “Not good enough,” is all he needs to say.