Superficial knowledge of subject Carol possesses (10)
I believe the answer is:
smattering
'superficial knowledge' is the definition.
(as in knowing a smattering of a language)
'subject carol possesses' is the wordplay.
'subject' becomes 'matter' (synonyms).
'carol' becomes 'sing' (I've seen this in other clues).
'possesses' means one lot of letters goes inside another.
'matter' going inside 'sing' is 'SMATTERING'.
'of' is the link.
(Other definitions for smattering that I've seen before include "Little bit" , "superficial knowledge" , "Tiny amount (of knowledge)" , "Dash" , "little knowledge" .)