One point about one numbskull (5)
I believe the answer is:
idiot
'numbskull' is the definition.
(I've seen this in another clue)
'one point about one' is the wordplay.
'one' becomes 'I' (Roman numeral).
'point' becomes 'dot' (synonyms).
'about' is an insertion indicator.
'one' becomes 'I' (Roman numeral).
'dot' placed around 'i' is 'diot'.
'i'+'diot'='IDIOT'
(Other definitions for idiot that I've seen before include "Garret" , "Dunce" , "Ass, ninny" , "Dope" , "Silly ass" .)