Country garment worn by knight (5)
I believe the answer is:
tonga
'country' is the definition.
(Tonga is an example)
'garment worn by knight' is the wordplay.
'garment' becomes 'toga' (toga is a kind of garment**).
'worn by' indicates putting letters inside (I've seen this in other clues).
'knight' becomes 'n' (chess).
'toga' placed around 'n' is 'TONGA'.
(Other definitions for tonga that I've seen before include "S.W Pacific Kingdom" , "Do a bad tango in the Pacific archipelago" , "Relatively small" , "two-wheeler" , "Islands once ruled by Queen Salote" .)