With knight for rook, end is imminent (4)
'imminent' is the definition.
'with knight for rook' is the wordplay.
'with' is a charade indicator (letters next to each other).
'knight' becomes 'n' (chess).
'for rook' becomes 'ear' (I can't explain this - if you can you should believe this answer much more).
'n' next to 'ear' is 'NEAR'.
'end is' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for near that I've seen before include "Tight-fisted", "Miserly; approach", "A short distance away", "(Get) close to", "Close in time or space".)