Extinction? Mostly ask questions of the French and America (7)
I believe the answer is:
quietus
'extinction?' is the definition.
(I've seen this before)
'mostly ask questions of the french and america' is the wordplay.
'mostly' means to remove the last letter.
'ask questions' becomes 'quiz'.
'of the french and' becomes 'et' ('and' in French).
'america' becomes 'us' (abbreviation for the United States).
'quiz' with its last letter taken away is 'qui'.
'qui'+'et'+'us'='QUIETUS'
(Other definitions for quietus that I've seen before include "Curtains" , "Extinction, death" , "peace" , "discharge" , "Final riddance - not quite quite us" .)