At the threshing floor, what did Ruth ask Boaz to do?

Answer: Spread his garment's corner over her

Ruth said, "Spread the corner of your garment over me, for you are a kinsman-redeemer" (KJV: "spread thy skirt").

“At midnight, Boaz was startled, turned over, and there lying at his feet was a woman! “Who are you?” he asked. “I am your servant Ruth,” she replied. “Spread the corner of your garment over me, for you are a kinsman-redeemer.””— Ruth 3:8-9 (BSB)