FIG. 1 is a perspective view from below and in front of the knee pad; FIG. 2 is a perspective view from above and behind the knee pad thereof; FIG. 3 is a front view thereof; FIG. 4 is a left side view thereof; the right side view being a mirror image; FIG. 5 is a rear view thereof; FIG. 6 is a top view thereof; and, FIG. 7 is a bottom view thereof. The broken lines depict portions of the knee pad that form no part of the claimed design.