The ornamental design for a knife, as shown and described.
FIG. 1 is a front perspective view of a knife, showing my new design in an open position, the broken lines representing environment and forming no part of the claim design;
FIG. 2 is a top plan view of the invention illustrated in FIG. 1;
FIG. 3 is a front elevation view of the invention illustrated in FIG. 1;
FIG. 4 is a left elevation view of the invention illustrated in FIG. 1;
FIG. 5 is a bottom plan view of the invention illustrated in FIG. 1;
FIG. 6 is a rear elevation view of the invention illustrated in FIG. 1;
FIG. 7 is a right elevation view of the invention illustrated in FIG. 1; and,
FIG. 8 is front elevation view of the invention illustrated in FIG. 1, in a closed position.