It sounds to me like he does not know what the Item in question is, but want's to remove all of the duplicates so there is only one of each item in the list.
I threw this together just now:
(Defun RemoveDuplicates ( LST / item return)
(While LST
(SetQ item (Car LST)
LST (Cdr LST )
)
(SetQ LST (VL-Remove item LST) )
(SetQ return (Cons item return) )
)
(Reverse return )
)