We claim the ornamental design for a door knob, as shown and described.
FIG. 1 is a perspective view of an embodiment of the claimed design;
FIG. 2 is a front view of the embodiment of the claimed design shown in FIG. 1;
FIG. 3 is a rear view of the embodiment of the claimed design shown in FIG. 1; and,
FIG. 4 is a side view of the embodiment of the claimed design shown in FIG. 1.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design. Broken lines formed by equal length dashes show unclaimed portions of the design. Broken lines formed of unequal length dashes (i.e., dash-dot) show boundaries between claimed and unclaimed portions of the design.