The ornamental designs for disk wheel cover, as shown and described.
FIG. 1 is a perspective view of a disk wheel cover showing my first new design;
FIG. 2 is a front elevational view thereof; and,
FIG. 3 is a partial (elemental) enlarged view thereof.
The broken line showing of the rear of the wheel is included for the purpose of illustrating environment and forms no part of the claimed design. The dash dot line on either side of the partial view in FIG. 3 is for the purpose of illustrating the boundary of the claimed design and forms no part thereof.