Knight and king found in beer joint (5)
I believe the answer is:
ankle
'joint' is the definition.
(joint of the body)
'knight and king found in beer' is the wordplay.
'knight' becomes 'n' (chess abbreviation).
'and' is a charade indicator (letters next to each other).
'king' becomes 'K' (chess abbreviation).
'found in' is an insertion indicator.
'beer' becomes 'ale' (type of beer).
'n'+'k'='nk'
'nk' inserted within 'ale' is 'ANKLE'.
(Other definitions for ankle that I've seen before include "Major joint in lower limb" , "Foot-leg connector" , "Lower leg joint" , "Major foot joint" , "Bone over foot" .)