Amusing or otherwise, he has a lot to learn (9)
I believe the answer is:
ignoramus
'he has a lot to learn' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'amusing or otherwise' is the wordplay.
'otherwise' indicates anagramming the letters.
'amusing'+'or'='amusingor'
'amusingor' is an anagram of 'IGNORAMUS'.
Can you help me to learn more?
(Other definitions for ignoramus that I've seen before include "Ron is a mug (anag.)" , "Dimwit" , "One who knows nothing" , "One could be blissful it's said" , "Uninformed sort" .)