The ornamental design for a trainable dolly, as shown and described.
FIG. 1 is a top frontal perspective view of a trainable dolly according to the new design;
FIG. 2 is a front view of the trainable dolly shown in FIG. 1;
FIG. 3 is a back view of the trainable dolly shown in FIG. 1;
FIG. 4 is a left side view of the trainable dolly shown in FIG. 1;
FIG. 5 is a right side view of the trainable dolly shown in FIG. 1;
FIG. 6 is a top view of the trainable dolly shown in FIG. 1; and,
FIG. 7 is a bottom view of the trainable dolly shown in FIG. 1.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design.