Talk about king’s clothing (4)
I believe the answer is:
garb
'clothing' is the definition.
(I know that garb is a type of clothing)
'talk about king's' is the wordplay.
'talk' becomes 'gab' (I've seen this in another clue).
'about' means one lot of letters goes inside another.
'king' becomes 'R' (abbreviation of Latin rex).
'gab' placed around 'r' is 'GARB'.
(Other definitions for garb that I've seen before include "Fashion of dress" , "Attire, clothing" , "something to wear" , "Dress - clothing" , "Raiment" .)