The ornamental design for a knifeholder for dishwasher, as shown and described.
FIG. 1 is a perspective view of a knife holder for dishwasher showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a perspective view thereof while in use on a dishwasher rack.
The broken lines represent environmental structure or unclaimed portions of the knife holder for dishwasher and do not form a part of the claimed design.