Talk about king's plan (5)
I believe the answer is:
chart
'plan' is the definition.
(I've seen this before)
'talk about king's' is the wordplay.
'talk' becomes 'chat' (I've seen this before).
'about' means one lot of letters goes inside another.
'king' becomes 'r' (r is abbreviation for rex).
'chat' placed around 'r' is 'CHART'.
(Other definitions for chart that I've seen before include "Marine map" , "Table or diagram" , "Visual display of information" , "what could be a pie" , "[LOVE ME DO] became the first of many to ..." .)