How Do you Answer This puedes jugar al tenis manana?

It depends on what your schedule is and whether or not you can play tennis. If you CAN play tennis and your schedule IS free, you could say, "Si. Me encantaría. A qué hora?" Which means, "Yes. I'd be delighted. What time?" If, on the other hand, you can't play tennis, and your schedule is full, you might say, "Lo siento. No juego ténis, y además mi horario está lleno." Which means, "I'm sorry. I don't play tennis, and besides, my schedule is full."