The ornamental design for a holder for cookies, as shown and described.
FIG. 1 is a top perspective view of a holder for cookies showing my new
design;
FIG. 2 is a right side elevational view thereof, the undisclosed left side
being substantially the same;
FIG. 3 is a front elevational view thereof, with a cookie shown in broken
lines for illustrative purposes only and forming no part of the claimed
design;