Mark wants knitted garment shortened (4)
I believe the answer is:
scar
'mark' is the definition.
(mark left by an injury)
'knitted garment shortened' is the wordplay.
'knitted garment' becomes 'scarf' (scarves are often knitted).
'shortened' means to remove the last letter.
'scarf' with its last letter taken off is 'SCAR'.
'wants' is the link.
(Other definitions for scar that I've seen before include "Craggy outcrop" , "Mark left by injury" , "Mark of old injury" , "Old-wound mark" , "Mark of a wound remaining on the skin" .)