I have sole custody of my daughter. My ex has 1 Saturday visit from 9-9 supervised visits. If something happens to me? Does he automatically get custody or can I dictate in my will

Neither. You can express a preference in your will but its not binding. A child is not property that can be willed. If a court required supervised visits then it certainly wouldn't be automatic that he would be awarded custody. A court would have to review the situation.