The words "madness" and "folly" have similar meanings and refer to foolish thinking and behavior, respectively. See how you translated this in [Ecclesiastes 1:17](../01/17.md). (See: [[rc://en/ta/man/translate/figs-doublet]])
The author uses this rhetorical question to emphasize his point that the next king will not be able to do anything more valuable that what he had already done. This question can be written as a statement. Alternate translation: "For the next king who comes after the king can do nothing that a king before him has not already done." (See: [[rc://en/ta/man/translate/figs-rquestion]])