To answer my own question somewhat... I found there are some "meta" videos about street epistemology. I found this one A Humanitarian Option for Changing Minds by Anthony Magnabosco helpful. I also watched a few other actual "sessions" and found a common theme is getting the person to assign their own confidence level in whatever they are claiming to believe. Another seems to be not to actively initiate the discussion or pick the topic, let them come to you and say what they want to talk about. Another "trick" is if someone claims belief is based on feelings ask them if someone had the same feelings about something else (like a different holy book or god) would that make that it true. That feels a bit like epistemological "whataboutism" but it seems to work.

I'd be interested to know if someone has ever managed to pull off an online form of this ie. "online epistemology" because it really feels like the interpersonal interaction aspect is crucial...

I would say that if you have never been involved in such talks with theists, then you have been lucky. And that a better way to spread the idea of sceptical thinking, is to set a good example of being a good human being, while being open about your lack of faith in the supernatural.

However should you get involved, there are I think two mistakes to avoid when debating with theists.

Firstly. Do not get in debates about the existence or none existence of god, in the abstract, you may think that the fact that they can not 'prove' objectively, the existence of god is a weakness of theirs. But they think that the fact that you can not, disprove it either, is your greatest weakness. The fact is, nobody can objectively prove or disprove anything, at all, even existence, about something which is invisible by definition. ( As Bertrand Russel put it. There is a china teapot orbiting in space, half way between the Earth and the Sun. Prove there is not? ) But if you allow them to debate on that issue, then they will, in their own minds, having got no disproof of god out of you, claim the debate by default, and assume that no disproof is the same as proof, and that an abstract god is equivalent to their own particular brand of theist god in their holy book. Its one of their greatest delusions, to assume that the word god, by default means their own god. You have to remember that they are not really trying to prove the existence of god, they are trying to prove, the existence of 'their' god. Therefore keep the debate on the evidence they are using for that gods nature, in other words as found in their holy book.

Secondly. Do not be afraid of saying. "I don't know." as often as you can, and that you are happy to accept not knowing. It annoys the s##t out of them, and kills nearly all their arguments. Because remember, it is they who are making false claims of knowledge, based on pseudo-authority: They know god exists, they know how the universe began, they have the final word on morality, they know what happens to them after death, etc. , and all with only the evidence in some old badly rewritten, edited and translated book. If for example they ask you say, (assuming creationists ) how did the universe started, you can say, the big bang or whatever, then they will start asking you about your evidence about before the big bang, and then you are going round in circles. Instead say I don't think anyone knows, and then ask them for their proof which you can attack, because they are the ones making dishonest claims of knowledge and plain simple honesty is something they have no answer for.

The socratic method would need to be used with less vigour when dealing with most people, for religious views and emotions are often strongly connected. Those of faith may well become very defensive very quickly.
That said, there is a place for what you propose. Where do you start? It depends on what the person tells you about their religious views. Find out what the basis of them coming to faith was; was it belief in the Bible, the historicity of the resurrection, a religious experience, or... ? Then ask questions that gently probe that basis.

Well, I would start with, "How do you know that to be true?" and go from there, I guess. If the answer is something like "Because it's in my holy book," the next logical question would be "and how do you know that the book is true?"

The answers I've gotten to that question about the book have taken three main paths: self-referential ("it SAYS it's the word of God!" ), historical/archeological: ("archeologists have found the ruins of x, just like my book described" ), and revelation ("God talks to me and told me so" ).

To the self-referential, I might ask "aren't there other books that also say they're the words of God?". To the archeological, I might ask "do the ruins of a city prove that your book is true, or do they just prove that the city was known to the author of the book? I mean, Charleston is a real city, and the Civil War happened - but we know that Scarlett O'Hara was a fictional character." To the claim of revelation, I might ask "How do you know that was God speaking?"

I've never encountered someone whose religion was NOT based on a book, but I've heard that they exist. I haven't given much thought to what I might ask them.

Download the app Atheos. It's about what to say or ask believers.

If I want to make believe I'll watch something on Comet.