Name a trio composed by a top journalist (6)
I believe the answer is:
editor
'a top journalist' is the definition.
(I've seen this before)
'name a trio composed by' is the wordplay.
'name' becomes 'ed' (short for edward).
'composed' indicates anagramming the letters.
'by' means one lot of letters go next to another.
'trio' is an anagram of 'itor'.
'ed'+'itor'='EDITOR'
(Other definitions for editor that I've seen before include "cutter?" , "One responsible for leader" , "One is in charge of publication" , "Newspaper or publication chief" , "Or tied up my boss" .)