Who, in French, takes online exam, perhaps most subdued in conversation? (8)
I believe the answer is:
quietest
'perhaps most subdued in conversation?' is the definition.
'who in french takes online exam' is the wordplay.
'who in french' becomes 'qui' ('who' in French).
'takes' says to put letters next to each other.
'online' becomes 'e' (as in e-mail or e-commerce).
'exam' becomes 'test' ('test' can be a synonym of 'exam').
'qui'+'e'+'test'='QUIETEST'
(Other definitions for quietest that I've seen before include "making least noise?" , "Most unobtrusive" .)