The question of a model? (5)
I believe the answer is:
poser
I believe this is a double definition.
'the question' is the first definition.
(poser is a kind of question)
'a model?' is the second definition.
('poser' can be a synonym of 'model')
'of' is the link.
(Other definitions for poser that I've seen before include "Question - a sitter" , "Puzzling question about ropes" , "Hard question" , "What's difficult" , "Toughie" .)