Model in quiet bar popped the question (8)
I believe the answer is:
proposed
'popped the question' is the definition.
('propose' can be a synonym of 'pop the question')
'model in quiet bar' is the wordplay.
'model' becomes 'pose' (model can mean to pose).
'in' means one lot of letters goes inside another.
'quiet bar' becomes 'prod' (I can't justify this - if you can you should give a lot more credence to this answer).
'pose' placed into 'prod' is 'PROPOSED'.
Can you help me to learn more?
(Other definitions for proposed that I've seen before include "Asked to marry" , "Advocated" , "Suggested" , "Offered for consideration - perhaps marriage" , "Nominated, put forward for consideration" .)