Belong at paper, working with all the rage (9)
I believe the answer is:
appertain
'belong' is the definition.
(appertaining is a kind of belonging)
'at paper working with all the rage' is the wordplay.
'working with' is an anagram indicator (working with the letters).
'all the rage' becomes 'in' (both can mean trendy).
'at'+'paper'='atpaper'
'atpaper' with letters rearranged gives 'apperta'.
'apperta'+'in'='APPERTAIN'
(Other definitions for appertain that I've seen before include "Be relevant to" , "Bear on" , "Belong, relate (to)" , "Concern" .)