Though I respect the sincerity of the responder to his anonymous inquirer, the argument could address more than what he has already established here. The inquirer is asking for “proof” of God’s existence. First it must be asked what the inquirer means by “proof”. If he means scientific proof, then he is looking for something along the lines of some proposition (e.g. “God exists”) being empirically verified by means of observation, hypothesis, deduction, falsification, and etc.
Scientific proof (usually used in the flawed sense) is really a reference to a logical method of investigation known as induction. Induction is moving from specific examples to a general statement about the examples. For example, in a closed system things fall if not supported, hence gravity.
The limitation of this method is that unless one is working with an necessarily limited set (meaning that there is only a limited number of examples of the item one is generalizing about) one can never say that she has knowledge as a unknown example may not conform to the rule that one developed. This is why scientific method can never really provide knowledge strictly speaking and at best provides degrees of probability.
If he means philosophical proof, then the same proposition (“God exists”) could be substantiated on the basis of logical deduction. Lastly he could also be referring to historical proof, but that insists that God could be substantiated by some means of observable archaeological, paleontological [or what have you], evidence to where the historian can look and examine God’s existence that way. It is of course not by science nor historical methods can we “proof” the existence of God because God (according to traditional theism) cannot be verified by natural or empirical means, nor by detected by some method of historical discourse.
Philosophical proof, which may or may not include scientific claims, in its deductive form offers logical proof for a particular claim which, I am convinced, can actually be stronger than scientific proof. Legal proof is an evidence based medium that that offers criterion for what evidence is acceptable in support of a claim and can be very powerful proof in a given argument. Historical arguments have their own criterion for what rises to proof and though the arguments in this discipline are probability based, experts can and do distinguish between stronger and weaker probabilities.