Penning nothing, horribly tired journalist (6)
I believe the answer is:
editor
'journalist' is the definition.
(I've seen this before)
'penning nothing horribly tired' is the wordplay.
'penning' means one lot of letters goes inside another.
'nothing' becomes 'O' (looks like zero - 0).
'horribly' is an anagram indicator.
'tired' with letters rearranged gives 'editr'.
'o' put within 'editr' is 'EDITOR'.
(Other definitions for editor that I've seen before include "Senior journalist" , "Press fellow" , "One is in charge of publication" , "Chief journalist" , "Person who revises and prepares for publication" .)