According to 1 Chronicles 2:16, Zeruiah, the mother of Joab, Abishai and Asahel, was the sister of whom?

Answer: David

Jesse's daughters were Zeruiah and Abigail, so David's commander Joab and his brothers were David's own nephews.

“Jesse was the father of Eliab his firstborn; Abinadab was born second, Shimea third, Nethanel fourth, Raddai fifth, Ozem sixth, and David seventh. Their sisters were Zeruiah and Abigail. And the three sons of Zeruiah were Abishai, Joab, and Asahel.”— 1 Chronicles 2:13-16 (BSB)