Can you get pregnant if you have unprotected sex on the 8th day of a 28-32 days menstrual cycle?

Yes, but low chance: Since sperm can live for several days, and there's always a chance you can ovulate a day or two early, then it's possible. It's not likely, but it's possible. I had a patient who conceived from having sex while on the last day of her period. I've never forgotten that, and it will always affect my opinion of the "rhythm method".