Job finishes the rhetorical question that begins with the words "Who laid its cornerstone" in verse 6. This can be translated as a statement. "Tell me who laid its cornerstone when the morning stars ... the sons of God shouted for joy." (See: [[rc://en/ta/man/jit/figs-rquestion]])
The morning stars are spoken of as singing like people sing. Possible meanings are: 1) the "morning stars" are the same as the "sons of God" in the next line or 2) "the morning stars" refer to stars in the sky. (See: [[rc://en/ta/man/jit/figs-personification]])
The abstract noun "joy" can be translated as the adverb "joyfully." Alternate translation: "shouted joyfully" (See: [[rc://en/ta/man/jit/figs-abstractnouns]])