After seizing Samson and gouging out his eyes, what did the Philistines force him to do?

Answer: Grind grain in prison

They bound him with bronze shackles in Gaza and made him grind grain in the prison. Meanwhile his hair began to grow back.

“Then the Philistines seized him, gouged out his eyes, and brought him down to Gaza, where he was bound with bronze shackles and forced to grind grain in the prison. However, the hair of his head began to grow back after it had been shaved.”— Judges 16:21-22 (BSB)