Jonathan uses this question to emphasize that he will tell David if Saul intends to harm him. This rhetorical question can be translated as a statement. AT: "then I will certainly send to you and make it known to you" (See: [[rc://en/ta/man/translate/figs-rquestion]])
This is an idiom. Jonathan uses this oath for emphasis and speaks of himself as if he were another person. AT: "may Yahweh do to me whatever harm my father intends to do to you, and even more than that" (See: [[rc://en/ta/man/translate/figs-idiom]] and [[rc://en/ta/man/translate/figs-pronouns]])