The phrase "sent word" means that he sent a messenger to give a report. AT: "Joab sent a messenger to David to give a report" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Joab says that David may rebuke him by asking these rhetorical questions. These questions may be written as statements. AT: "You should not have gone so near to the city to fight. You should have known that they would shoot from the wall." (See: [[rc://en/ta/man/translate/figs-rquestion]])
This refers to men of the city shooting arrows down at their enemy from the top of the city wall. AT: "shoot arrows at you from the top of the city wall" (See: [[rc://en/ta/man/translate/figs-explicit]])