How do I call up someone to the Torah if he does not know his Hebrew name nor his father’s Hebrew name?
If he will keep a new Jewish name, then give him a Jewish name while calling him up to the Torah. If he won’t keep the name then call him up with his secular name.
He should be called up with the father’s name that he is familiar with, but you should try to verify if possible.
פשוט. וכ״כ בנתיבים בשדה השליחות ח”ב ע’ 69-70 מסברא.