The ornamental design for a knife, substantially as shown and described.
FIG. 1 is a perspective view of a knife showing my new design.
FIG. 2 is a front elevational view thereof.
FIG. 3 is a rear elevational view thereof.
FIG. 4 is a top plan view thereof.
FIG. 5 is a left side elevational view thereof.
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a right side elevational view thereof.
Stippling and shading lines shown in the drawings are intended to represent the approximate three-dimensional contour of the design, and are not intended to indicate surface decoration. Features not shown in the drawings, or features depicted in broken lines, form no part of the claimed design.