I claim the ornamental design for a spout head attachment for watering can, as shown and described.
FIG. 1 is a perspective view of the invention;
FIG. 2 is a top plan view of the invention;
FIG. 3 is a left side view of the invention; the right side view of the invention is identical to the left side view;
FIG. 4 is a front elevation of the invention;
FIG. 5 is a rear elevation of the invention;
FIG. 6 is a bottom plan view of the invention; and,
FIG. 7 is an environmental perspective view of the invention.
The broken lines in FIG. 6 represent portions of the spout head attachment for watering can that form no part of the claimed design, and the broken lines in FIG. 7 show environmental structure and form no part of the claimed design.