Whom did Joab send to persuade David to bring Absalom back?

Answer: A wise woman from Tekoa

Joab had her pose as a grieving widow and tell David a story. Afterward David told Joab, "Go, bring back the young man Absalom."

“So Joab sent to Tekoa to bring a wise woman from there. He told her, “Please pretend to be a mourner; put on clothes for mourning and do not anoint yourself with oil. Act like a woman who has mourned for the dead a long time.”— 2 Samuel 14:2 (BSB)