Turn to observe, or take a look (4)
I believe the answer is:
peek
'a look' is the definition.
(peek can mean to look at quickly)
'turn to observe' is the wordplay.
'turn' says the letters should be written backwards.
'to observe' becomes 'keep' ('keep' can be a synonym of 'observe').
'keep' reversed gives 'PEEK'.
'or take' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for peek that I've seen before include "Quick, sly look" , "Take brief or surreptitious look" , "Secret look" , "Repeatedly look like this" , "spy" .)