As a question word ('what / why / where') 奚 is purely classical, like 何. In modern Chinese you mostly meet it in 奚落 (to taunt; to ridicule).
culture
Capitalized, 奚 is also a surname and the name of the Xi, a Mongolic people of medieval north China. The character originally pictured a hand holding a roped captive, hence its old meaning of 'slave'.
