The ornamental design for a six spoke wheelcap, as shown and described.
FIG. 1 is a top front perspective view of a six spoke wheel cap, in accordance with an embodiment of the present invention;
FIG. 2 is a bottom perspective view of the six spoke wheel cap of FIG. 1;
FIG. 3 is a left side view of the six spoke wheel cap of FIG. 1;
FIG. 4 is a right side view of the six spoke wheel cap of FIG. 1;
FIG. 5 is a top view of the six spoke wheel cap of FIG. 1; and,
FIG. 6 is a bottom view of the six spoke wheel cap of FIG. 1.
Any broken lines, shown throughout in the drawing figures, are included for the purpose of illustrating environmental structures and form no part of the claimed design.