The author uses this rhetorical question to emphasize that no person truly knows what is good for man. This question can be written as a statement. Alternate translation: "No one knows what is good for a person ... he passes through like a shadow." (See: [[rc://en/ta/man/translate/figs-rquestion]])
This speaks of how life passes quickly by saying that it is like a shadow that quickly disappears. The phrase "numbered days" emphasizes that a person's life is short. Alternate translation: "during his futile, short life, which he passes through as quickly as a shadow passes by" (See: [[rc://en/ta/man/translate/figs-simile]])
The author uses this rhetorical question to emphasize that no one knows what will happen after a person dies. This question can be written as a statement. Alternate translation: "No one can tell a person ... after he is gone." (See: [[rc://en/ta/man/translate/figs-rquestion]])
This refers to things that are done on earth. See how you translated "under the sun" in [Ecclesiastes 1:3](../01/03.md). Alternate translation: "what will happen on the earth" (See: [[rc://en/ta/man/translate/figs-idiom]])