The ornamental design for a worktable, as shown and described.
FIG. 1 is a front perspective view of a worktable showing my new design; and,
FIG. 2 is a rear perspective view thereof.
The bottom surfaces of the worktable are not illustrated as they form no part of the claimed design. The sides, ends and top portion of the leg supports are not illustrated as they form no part of the claimed design.