The ornamental design for a jig for dental prosthesis, as shown and described.
FIG. 1 is a perspective view of a jig for dental prosthesis, showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a left side view thereof.
The broken lines shown in the drawings present portions of the jig for dental prosthesis that form no part of the claimed design. All sides not shown form no part of the claimed design.