Backwards-looking study describing duke gone over again (9)
I believe the answer is:
retrodden
'gone over again' is the definition.
(trod over again)
'backwards-looking study describing duke' is the wordplay.
'backwards-looking' becomes 'retro' (retro means looking back to the past).
'study' becomes 'den' (term for a study or office).
'describing' is an insertion indicator (describe can mean to form the outline of).
'duke' becomes 'd' (abbreviation).
'den' placed around 'd' is 'dden'.
'retro'+'dden'='RETRODDEN'
(Other definitions for retrodden that I've seen before include "being passed over again" , "walked over again" .)