A rhetorical device refers to a technique used to persuade the audience about an idea and that reinforces the main point in a speech. In the case of rhetorical questions, these are questions the speaker asks the audience without expecting them to answer them, as rhetorical questions are used to make the audience understand or think about a point. This is the technique used in the case of a speaker that asks multiple times "Who knows?" as the speaker does not expect this question to be answered but might use it to reinforce a point such as reinforcing doubt about a set of statements.
