He could mention the moral arguments... but each man of conscience can recognize these also, outside any religious belief.
He could maybe unfold some modern scientific arguments which indeed, point to the existence of an intelligent and incredibly careful creator... but the nonbeliever may easily observe that none of them implies that this mysterious creator incarnated himself as a man in order to bring the example of divine love to mankind and ensure its salvation.
He could enumerate the prophecies of the Old Testament, also confirmed by the ancient Dead Sea Scrolls, which find their fulfillment in the life of Jesus, as it is described in Gospels. However, these ones will usually not attract the unbeliever, for he already heard other theories which seem to demonstrate irrefutably the fallacies and contradictions of the Scriptures.
Opinions and Testimonies
of believers in the New Revelation as the Lord's direct Word