The ornamental design for frunk cover or gate, as shown and described.
FIG. 1 is a front perspective view of a frunk cover or gate on a vehicle;
FIG. 2 is an enlarged view of the portion of FIG. 1 depicting the frunk cover or gate;
FIG. 3 is a front orthogonal view of the frunk cover or gate; and,
FIG. 4 is a side orthogonal view of the frunk cover or gate.
The broken lines present in the drawings are included for the purpose of illustrating portions of the article which form no part of the claimed design.