The ornamental design for a portion of a shoe, as shown and described.
FIG. 1 is a left side elevational view of a shoe showing my new design;
FIG. 2 is a right side elevational view thereof; and,
FIG. 3 is a rear elevational view thereof.
The broken lines within the solid lines of the claimed design are illustrative of a design that may be incorporated within the boundaries of, but does not form a part of, the claimed design. All other broken lines represent the remaining portions of the shoe. The broken lines are for illustrative purposes only and form no part of the claimed design.