Is it the shot glass at the top that's stuck or the whole top lid bit? Generally if something is screwed on too tight you can tap it on the side of a table/bench around the circumference and that will make it slightly looser. You could also try undoing it with a towel between the shaker and your hand to give more friction. Or try jimmying it undone with a knife.
I managed to open it and it was the whole thing at the top. because it was new and hardly used until that day! ut now it's okay thanks Renee?? :)