Difficult question for model (5)
I believe the answer is:
poser
I believe this clue is a double definition.
'difficult question' is the first definition.
(I've seen this before)
'model' is the second definition.
('poser' can be a synonym of 'model')
'for' is the link.
(Other definitions for poser that I've seen before include "Puzzling question for the model" , "What's difficult" , "difficult puzzle" , "Exhibitionist" , "Show-off" .)