Try to extract everything from onion (4)
I believe the answer is:
shot
'try' is the definition.
(both can mean an attempt)
'everything from onion' is the wordplay.
'everything' becomes 'all' (all things).
'from' indicates named letters should be taken away.
'onion' becomes 'shallot' (shallot is a kind of onion).
'shallot' with 'all' removed is 'SHOT'.
'to extract' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for shot that I've seen before include "Knackered" , "Sent a bullet" , "Attempt (to kill?)" , "Wounded" , "Discharged a weapon" .)