I’ve known various theists, and don’t need do anything special to talk to them. I’ve tried having forms of the “why do you believe?” conversation with them over the years, but it doesn’t go very far. It always ends up in an argument from faith – “I believe, and that’s all I need” or an argument from inertia e.g. “the Church plays an important role in society”.
The problem with the “argument from inertia” is that it only covers the way things are, not the way things could or should be. Not everyone is an idealist or a Utopian who believes in improvement In other words, the religion fits their Panglossian nature, so when you argue against religion, you have to be careful that you aren’t coming across as insulting them personally, or a “party pooper”. I would first try to get them interested in the ways that religion makes the world a worse place, and try to get them to see that this is not the best of all possible worlds.
What they believe and why they believe it. I don’t know of many other questions that are relevant or that would apply to all of them.
Of course, it wouldn’t end there. I don’t give up after the simple answers. I’d likely lead them down a path of Socratic questioning until we get to the true root of their belief – which, in my experience, is that you just have to take it on faith. At which time I’d point out that if faith has no grounding in objective evidence, then all faiths are equally justified (i.e., not at all).