The idiom "to speak in someone's ear" means to speak where they can hear you. Alternate translation: "where the people who are on the wall may hear us" (See: [[rc://en/ta/man/translate/figs-idiom]])
This means that they are standing on the wall. The top of the wall was wide and a place where people could sit or stand. The full meaning of this statement can be made clear. Alternate translation: "who are standing on the wall" (See: [[rc://en/ta/man/translate/figs-explicit]])