The implicit answer is that he cannot understand it. This rhetorical question may be written as a statement. Alternate translation: "therefore, a person cannot understand his way" (See: [[rc://en/ta/man/translate/figs-rquestion]])
This is an idiom. The phrase "his way" refers to the person's life. Alternate translation: "understand why some things happen in his life" (See: [[rc://en/ta/man/translate/figs-idiom]])