Nag with repeated notes read aloud (3-3)
I believe the answer is:
gee-gee
'nag' is the definition.
(I've seen this in another clue)
'repeated notes read aloud' is the wordplay.
'repeated' shows that letters should be duplicated.
'notes read aloud' becomes 'gee' (I can't justify this - if you can you should give a lot more credence to this answer).
'gee' duplicated is 'GEE-GEE'.
'with' is the link.
(Other definitions for gee-gee that I've seen before include "Horse (slang)" , "Child's repetitive name for horse" , "Child's word for a horse" .)