The ornamental design for a desklamp, as shown and described.
FIG. 1 is a perspective view of a desk lamp showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The dashed or broken lines shown in the drawings depict portions of the desk lamp in which the design is embodied that form no part of the claimed design.