Composer to mark late unfinished note (9)
I believe the answer is:
scarlatti
'composer' is the definition.
(I've seen this before)
'mark late unfinished note' is the wordplay.
'mark' becomes 'scar' (mark left by an injury).
'unfinished' means to remove the last letter.
'note' becomes 'ti' (musical note as in do re mi fa so la ti).
'late' with its last letter removed is 'lat'.
'scar'+'lat'+'ti'='SCARLATTI'
'to' is the link.
(Other definitions for scarlatti that I've seen before include "Cantatas by him?" , "Italian scoring" , "Alessandro and Domenico --, Italian composers" , "opera producer" , "Italian composer of many keyboard works" .)