en_tn_lite_do_not_use/ecc/01/03.md

What profit does mankind gain ... under the sun?

The author uses this rhetorical question to emphasize that man's work is pointless and has no lasting benefit. This question can be written as a statement. Alternate translation: "Mankind gains no profit ... under the sun." (See: rc://en/ta/man/translate/figs-rquestion)

under the sun

This refers to things that are done on earth. Alternate translation: "on the earth" (See: rc://en/ta/man/translate/figs-idiom)