Organ is present from Cockney, we’re told (3)
I believe the answer is:
ear
'organ' is the definition.
(ear is a kind of organ)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for ear that I've seen before include "That makes sense" , "Lughole" , "Lend one and listen" , "See 24" , "good sense of music" .)