What is your religion?

Is it rude to ask someone what their religion is?

Or perhaps that's not exactly the issue. Maybe it's better to ask, what they believe in. Who do they worship?
God? do they create partners for God? Or do they worship the world instead?

Maybe elaborating the question is uncalled for? That's like nagging already - if the person has not answered the first question.

It seems to me that discussion about faith and religion is like a taboo in Singapore. People feel like it's very private. Or they feel ashamed to talk about it.. or they don't really think about it in the first place.