Producer of musical scores? Yes! (6)
I believe the answer is:
bartok
'producer of musical scores? yes' is the definition.
The definition suggests a singular noun which matches the answer.
'producer of musical scores? yes' is the wordplay.
'producer of musical scores?' becomes 'Bart' (songwriter Lionel Bart).
'yes' becomes 'ok' (both are affirmative answers).
'bart'+'ok'='BARTOK'
(Other definitions for bartok that I've seen before include "Bela -, nineteenth and twentieth century Hungarian composer" , "Hungarian-born composer, d. 1945" , "Bark to attract great Hungarian composer" , "Hungarian composer of folk music" , "Bela ------ (1881-1945), Hungarian composer" .)