A portrait I know less about (8)
I believe the answer is:
likeness
'a portrait' is the definition.
(I've seen this before)
'i know less about' is the wordplay.
'know' becomes 'ken' (I've seen this in another clue).
'about' indicates putting letters inside.
'i'+'ken'='iken'
'iken' going inside 'less' is 'LIKENESS'.
(Other definitions for likeness that I've seen before include "Similitude" , "Similarity in appearance" , "Picture" , "Similarity - faithful portrait" , "depiction" .)