As a humorist, he's quite a card (5)
I believe the answer is:
joker
'card' is the definition.
(joker is a type of playing card)
'as a humorist he's quite a' is the wordplay.
I cannot quite understand how this works, but
'he' could be 'ker' and 'ker' is found in the answer.
The remaining letters 'jo' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for joker that I've seen before include "Humorist" , "Buffoon" , "may appear wild in play" , "Pack's extra card" , "trickster" .)