The ornamental design for a knife, as shown and described.
FIG. 1 is a front elevational view of the knife in accordance with an embodiment of the present design, the rear side view being the mirror image of FIG. 1;
FIG. 2 is a left side elevational view of the knife illustrated in FIG. 1;
FIG. 3 is a right side elevational view of the knife illustrated in FIGS. 1-2;
FIG. 4 is a top plan view of the knife illustrated in FIGS. 1-3; and,
FIG. 5 is a bottom plan view of the knife illustrated in FIGS. 1-4.