Memory's returning before exam for most clever (8)
I believe the answer is:
smartest
'most clever' is the definition.
('smart' can be similar in meaning to 'clever')
'memory's returning before exam' is the wordplay.
'memory's' becomes 'rams' (RAM is an example).
'returning' says the letters should be written backwards.
'before' is a charade indicator (letters next to each other).
'exam' becomes 'test' ('test' can be a synonym of 'exam').
'rams' reversed gives 'smar'.
'smar'+'test'='SMARTEST'
'for' is the link.
(Other definitions for smartest that I've seen before include "Most wise" , "Cleverest; most chic" , "Most intelligent or most stylish" , "Brightest or best dressed" , "Extremely bright" .)