Quid sibi vult means “what does it mean.” Can you say quid tibi vis to mean what do you mean? Either way, what is the best way in Latin to say, “what do you mean.”
I’m taking these from Andreas Fritsch’s Index Sententarium Ac Locutionum: Handbuch lateinischer Sätze und Redewendungen. I haven’t looked up the citations, just passing them on:
quid tibi vis, insane? HOR. sat. 2,6,29
quid tibi vis, Marce Cato? SEN. epist. 14,13
quid tibi vis? TER. Eun. 559; 804; 1007
Gratias tibi ago secundo tuum ob adiutorium, mi amice.
It’s more than just “what does it mean”. Idiomatically it could be " what is he getting at? or even “WTF?” 