I claim the ornamental design for a anchoring unit for a parapet wall block, as shown and described.
FIG. 1 is a perspective view of the anchoring unit for a parapet wall block of my design shown in its ordinary environment when in use, assembled together with a corresponding facing unit for a parapet wall block;
FIG. 2 is a perspective view of the anchoring unit for a parapet wall block of my design;
FIG. 3 is a top plan view thereof, the bottom plan view being a mirror image;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a rear elevation view thereof; and,
FIG. 6 is a left end view thereof, the right end view being a mirror image.
Where included, broken lines showing environment or structure are for illustrative purposes only and form no part of the claimed design.