The ornamental design for a learning displaydevice, as shown and described.
FIG. 1 is a perspective view of the learning display device;
FIG. 2 is a top plan view of the learning display device;
FIG. 3 is a front elevation view of the learning display device; and,
FIG. 4 is a left side elevation view of the learning display device.
The rear and the bottom surfaces of the device are unadorned and form no part of the design. The right side elevation view is the mirror image of the left side elevation view.
The broken lines are included for the purpose of illustrating portions of the learning display device that forms no part of the claimed design.