This knot signifies that the wearer earned the Arrow of Light Award as a Webelos, the highest rank of Cub Scouting.
Scouts wear the Arrow of Light rank emblem centered just below the left pocket. Scouters wear the square knot symbol centered above the left pocket.
Where does it all go? See the BSA Insignia Guide for help in placing your Scout insignia and patches in the right place on your uniform.