Who's enemy in the valley with king (5)
I believe the answer is:
dalek
'who's enemy' is the definition.
'dalek' can be an answer for 'enemy' (I have seen 'Alien enemy' mean 'dalek' so perhaps 'enemy' could also mean 'dalek'). I'm unsure of the 'who's' bit.
'valley with king' is the wordplay.
'valley' becomes 'dale' (dale is a kind of valley).
'with' is a charade indicator (letters next to each other).
'king' becomes 'k' (abbreviation for king in chess).
'dale'+'k'='DALEK'
'in the' acts as a link.
Can you help me to learn more?
(Other definitions for dalek that I've seen before include "Dr Who's alien robot" , "Hostile alien" , "SF villain" , "Doctor Who adversary" , "Doctor Who creature" .)