Using some kohlrabi's questionable in this (6)
I believe the answer is:
bisque
'this' is the definition.
The definition suggests a singular noun which matches the answer.
'using some kohlrabi's questionable in' is the wordplay.
'using some' indicates a hidden word.
'BISQUE' can be found hidden inside 'kohlrabis questionable in'.
(Other definitions for bisque that I've seen before include "golf handicap" , "Cream soup made with shellfish" , "pot?" , "Thick shellfish soup" , "Shellfish soup - kind of pottery" .)