If this would be translated to English, the direct way of questioning would be:
What number president was Cory?
or
What number president is Cory?
You can ask your friends this way like in casual conversations. But if it's somebody that you don't think you can be casual with, try the alternatives below:
1. Where does Cory fall numerically in the list of presidents of the Philippines?
2. Numerically, where does Cory fall on the list of Philippine presidents?
3. Based on the number of Philippine presidents which position does Cory hold?