The ornamental design for a skateboard apparatus, as shown and described.
FIG. 1 is a perspective view of a new design for a skateboard apparatus;
FIG. 2 is a top plan view thereof;
FIG. 3 is a partial cross sectional view thereof, taken from line 3-3 in FIG. 2, showing a textured transparent layer covering a gel pad layer on the top surface of the skateboard apparatus;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a front elevation view thereof;
FIG. 6 is a rear elevation view thereof; and,
FIG. 7 is a right side view thereof.
The phantom lines in the drawings represent unclaimed subject matter.