The ornamental design for a cookingplate, as shown and described.
FIG. 1 is a front view of a cooking plate, showing our new design;
FIG. 2 is rear view thereof;
FIG. 3 is first side view thereof;
FIG. 4 is second side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is bottom view thereof; and,
FIG. 7 is a perspective view thereof.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design while all other broken lines are directed to unclaimed portions; the broken lines form no part of the claimed design.