Instrument study sure to leave answer to the end (10)
I believe the answer is:
concertina
'instrument' is the definition.
(concertina is a kind of instrument)
'study sure to leave answer to the end' is the wordplay.
I cannot really see how this works, but
'study' could be 'con' (con can mean to study) and 'con' is found within the answer.
'answer' could be 'a' (abbreviation eg in Q and A) and 'a' is located in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for concertina that I've seen before include "Instrument played like an accordion" , "Squeeze box" , "Squeeze-box" , "fold" , "Musical instrument with bellows" .)