The claimed design is directed solely to the shape and configuration of the cocktail jigger as shown in the figures and is not intended to be limited to any particular surface ornamentation on or color of the cocktail jigger. Portions or features of the cocktail jigger not shown in the drawings form no part of the claimed design. The evenly dotted broken lines in the drawings illustrate unclaimed features of the cocktail jigger and form no part of the claimed design.