The ornamental design for LED lamp wick, as shown and described.
FIG. 1 is perspective view showing my design;
FIG. 2 is another perspective view showing my design
FIG. 3 is a front view showing my design;
FIG. 4 is a back view showing my design;
FIG. 5 is a left side view showing my design;
FIG. 6 is a right side view showing my design;
FIG. 7 is a top plan view showing my design; and,
FIG. 8 is a bottom plan view showing my design.
The broken line showing of an LED lamp wick is included for the purpose of illustrating portions of the article that form no part of the claimed design.