Dubbing grand knight I knight, say, in retrospect (6)
I believe the answer is:
naming
'dubbing' is the definition.
(to dub is to give a name)
'grand knight i knight say in retrospect' is the wordplay.
'grand' becomes 'G' (G is short for ground as in a thousand).
'knight' becomes 'N' (chess abbreviation).
'knight say' becomes 'man' (knight is a kind of man).
'in retrospect' shows that the letters should be reversed in order.
'g'+'n'+'i'+'man'='gniman'
'gniman' back-to-front is 'NAMING'.
(Other definitions for naming that I've seen before include "Calling" , "Conferring appellation on" , "Identifying, citing" , "Allotting term to" , "Identifying; mentioning" .)