Question about English dairy product? (4)
I believe the answer is:
whey
'dairy product' is the definition.
(I know that whey is a type of dairy product)
'question about english' is the wordplay.
'question' becomes 'why' (why is a question word).
'about' is an insertion indicator.
'english' becomes 'e' (abbreviation).
'why' enclosing 'e' is 'WHEY'.
(Other definitions for whey that I've seen before include "Residual liquid from clotted milk" , "Watery part of milk after curd separation" , "Watery content of milk" , "Watery residue of milk" , "Watery dairy product" .)