Amusing or otherwise, he's a dunce (9)
I believe the answer is:
ignoramus
'a dunce' is the definition.
(I've seen this before)
'amusing or otherwise' is the wordplay.
'otherwise' indicates anagramming the letters.
'amusing'+'or'='amusingor'
'amusingor' anagrammed gives 'IGNORAMUS'.
'he's' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for ignoramus that I've seen before include "One is not intelligent" , "I wouldn't know" , "Imbecile" , "One who knows nothing" , "A know-nothing" .)