Friend occupied by certain upcoming examination (7)
I believe the answer is:
perusal
'examination' is the definition.
(I've seen this in another clue)
'friend occupied by certain upcoming' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'occupied by' indicates putting letters inside (inserted letters occupy or enter the word).
'certain' becomes 'sure' (synonyms).
'upcoming' shows that the letters should be reversed in order (in a down clue coming up is backwards).
'sure' reversed gives 'erus'.
'pal' going around 'erus' is 'PERUSAL'.
(Other definitions for perusal that I've seen before include "thorough scan" , "Careful look" , "Process of examination" , "Inspection" , "Careful reading" .)