Take another look at donkeys put in reserve (8)
I believe the answer is:
reassess
'take another look at' is the definition.
(to reassess is to look at or evaluate again)
'donkeys put in reserve' is the wordplay.
'donkeys' becomes 'asses' (an ass is a donkey).
'put in' means one lot of letters goes inside another.
'reserve' becomes 'res' (I've seen this in other clues).
'asses' going within 'res' is 'REASSESS'.
(Other definitions for reassess that I've seen before include "Newly evaluate" , "Have second thoughts" , "Rate afresh" , "size up again" , "judge again" .)