The ornamental design for a pocket knife blade, as shown and described.
FIG. 1 is a right side elevational view of a pocket knife blade, showing my new design, wherein the broken line outline of the pocket knife handle and blade is for environmental purposes only and forms no part of the claimed design, and where the opposing left side view is a mirror image of FIG. 1.
FIG. 2 is a top plan view of the pocket knife blade shown in FIG. 1.
FIG. 3 is a bottom plan view of the pocket knife blade shown in FIG. 1.
FIG. 4 is a front view of the pocket knife blade shown in FIG. 1; and,
FIG. 5 is a rear view of the pocket knife blade shown in FIG. 1.