The ornamental design for the knife handle, as shown and described.
FIG. 1 is a side view of the present invention;
FIG. 2 is an enlarged side view of the present invention;
FIG. 3 is a top view of the present invention;
FIG. 4 is a bottom view of the present invention;
FIG. 5 is a front view of the present invention; and,
FIG. 6 is a back view of the present invention.
The broken line showing of the knife handle is included for the purpose of illustrating environmental structure and forms no part of the claimed design.