One blowing their own trumpet? (8)
I believe the answer is:
musician
'one blowing their own trumpet?' is the definition.
This is all the clue.
(Other definitions for musician that I've seen before include "Composer or performer of vocal or instrumental sounds" , "Composer, perhaps" , "Performer of music" , "Instrumentalist, player" , "Minus CIA, one can compose or play" .)