So dukes rise endlessly in prestige! (5)
I believe the answer is:
kudos
'endlessly in prestige' is the definition.
'kudos' can be an answer for 'prestige' (I've seen this before). I'm unsure of the 'endlessly in' bit.
'so dukes rise' is the wordplay.
'dukes' becomes 'duk' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'rise' says the letters should be written backwards.
'so'+'duk'='soduk'
'soduk' back-to-front is 'KUDOS'.
Can you help me to learn more?
(Other definitions for kudos that I've seen before include "Prestige; recognition" , "Acclaim" , "Fame - prestige" , "Praise and honours" , "Informal honour of glory" .)