Think domain as all the metals in the world.
Note :- glitter means “shines”
Understand meaning of each option in english below :-
Option A :- All the metals which glitter are not gold. (false because word “all” means gold are also included but gold always glitter)
Option B :- All the metals which are gold are glitter (although this statement is true but it not saying same thing as this statement “Not all that glitters is gold”)
Option C :- there exist a metal x which is gold but not glitter (this statement is always false)
Option D :- there exist a metal x which glitter but not gold (this is same statement that we have given in question)
So, option D is correct.