A Christian is walking with God, and preaching His word. Another person walks up and declares there is no God. Who has to prove their stance?
Neither. There is no actual request or demand for proof.
Same first person, but the second shouts “Prove it!” How would you prove it?
Ask them to join you on this journey of discovery, so that God may be revealed to them as He is revealed to you.
Proving it has to be equal or greater than your journey. It’s like a painter proving that they painted a picture. Either they have a witness for the whole session, a recording of the session, or you are ready to paint a new painting similar to the painting being challenged with this witness.
Allow them to ask questions, but work with them to find answers, so that they learn to find them too. We are building disciples, this is what discipleship looks like. It doesn’t just win one to Christ, it take one from the adversary.