I claim the ornamental design for a knife holder, as shown and described.
FIG. 1 is a front view of a knife holder of the claimed design;
FIG. 2 is a rear view of the knife holder shown in FIG. 1;
FIG. 3 is a right side view of the knife holder shown in FIG. 1;
FIG. 4 is a left side view of the knife holder shown in FIG. 1;
FIG. 5 is a top view of the knife holder shown in FIG. 1;
FIG. 6 is a bottom view of the knife holder shown in FIG. 1;
FIG. 7 is a front perspective view of the knife holder shown in FIG. 1; and,
FIG. 8 is a back perspective view of the knife holder shown in FIG. 1 holding knives, which are shown as environment in broken lines.
The ornamental design which is claimed is shown in solid lines in the drawings. Any broken lines in the drawings are for illustrative purposes only and form no part of the claimed design.