The ornamental design for a paletteknife, as shown and described.
FIG. 1 is a top view of the instant invention with the bottom view being a mirror image thereof. The broken lines are included for the purpose of illustrating a portion of the knife that forms no part of the claimed design;
FIG. 2 is a left side view of the instant invention. The broken lines are included for the purpose of illustrating a portion of the knife that forms no part of the claimed design; and,
FIG. 3 is a right side view of the instant invention. The broken lines are included for the purpose of illustrating a portion of the knife that forms no part of the claimed design.