Fall guy seen in dunce’s cap, ego attacked (9)
I believe the answer is:
scapegoat
'fall guy' is the definition.
(thesaurus)
'in dunce's cap ego attacked' is the wordplay.
'in' indicates a hidden word.
'SCAPEGOAT' can be found hidden inside 'dunces cap ego attacked'.
'seen' acts as a link.
(Other definitions for scapegoat that I've seen before include "Person taking blame for others" , "Can carrier" , "One made to take blame" , "Lay blame on" , "One is punished for the errors of others" .)