Poor complain endlessly about king's broadcast (8)
I believe the answer is:
proclaim
'broadcast' is the definition.
(thesaurus)
'poor complain endlessly about king's' is the wordplay.
'poor' indicates anagramming the letters.
'endlessly' means to remove the last letter.
'about' is an insertion indicator.
'king' becomes 'r' (r is abbreviation for rex).
'complain' with its last letter taken off is 'complai'.
'complai' is an anagram of 'poclaim'.
'poclaim' placed around 'r' is 'PROCLAIM'.
(Other definitions for proclaim that I've seen before include "Declare formally" , "Broadcast" , "Make a public announcement" , "advertise" , "Speak out" .)