Cut down knight in cold Danish city (8)
I believe the answer is:
condense
'cut down' is the definition.
(I've seen this before)
'knight in cold danish city' is the wordplay.
'knight' becomes 'N' (chess abbreviation).
'in' indicates putting letters inside.
'cold' becomes 'C' (eg on taps).
'danish city' becomes 'odense' (I've seen this before).
'c'+'odense'='codense'
'n' placed within 'codense' is 'CONDENSE'.
(Other definitions for condense that I've seen before include "Turn from gas to liquid" , "Abbreviate" , "Summarise" , "Make more concentrated, or express in fewer words" , "cut down" .)