The implicit answer here is "nothing." This question can be written as a statement. Alternate translation: "There is nothing that you know that we do not know." or "Everything you know, we also know." (See: [[rc://en/ta/man/jit/figs-rquestion]])
This speaks of the men having understanding as if it were something "inside" them. Alternate translation: "Everything you understand, we also understand." or "We understand everything that you understand." (See: [[rc://en/ta/man/jit/figs-rquestion]])