The ornamental design for a drinkingfountain, as shown and described.
FIG. 1 is a perspective view of a drinking fountain in accordance with our design;
FIG. 2 is a side elevational view of the drinking fountain as view from the right side in FIG. 1, with the left side elevational view being substantially identical;
FIG. 3 is a top plan view thereof;
FIG. 4 is a front elevational view, with the rear elevational view being substantially identical; and,