Suggest operation in writing (7)
I believe the answer is:
propose
'suggest' is the definition.
('propose' can be a synonym of 'suggest')
'operation in writing' is the wordplay.
'operation' becomes 'op'.
'in' is an insertion indicator.
'writing' becomes 'prose' (I've seen this in other clues).
'op' inserted into 'prose' is 'PROPOSE'.
(Other definitions for propose that I've seen before include "table" , "Pop the question" , "Tender" , "Present for consideration" , "Put forward (an idea)" .)