what number (in a sequence); what rank
Used to ask about the ordinal position of something in a list, queue, or ranking.
What number are you (in line)?
Where does this athlete rank in the world?
何番 asks 'what number' in a more general sense (e.g., bus number, phone number), while 何番目 specifically asks about the order or rank in a sequence.
Compound of 何 (what) + 番 (number) + 目 (ordinal suffix).