A diabetic person is fasting (qada ramadan fast) and before zuhr he experiences low blood sugar what should the person do? If the person breaks the fast, does he need to pay kaffara?

If he can't continue his fast due to his health condition then there is no kaffara for him. He has to fast later on if he will be able to do so. He has to pay fidiya (one meal) for that fast to a needy person.