The speaker is trying to convince the hearers that Hezekiah does not know how to defeat the Assyrians and would not have the might to carry out such a plan if he had one.
The speaker wants to make the hearers doubt that Egypt can support Judah. He does not ask this question looking for an answer. Alternate translation: "You cannot trust anyone to help you rebel against me." (See: [[rc://en/ta/man/jit/figs-rquestion]])