Should I ask if they have experince with complex ptsd and relgious cults? I seem to find someone with expertise in ptsd but no idea how to deal with the religious aspect and how it affected everything
I think anything that's important to you is a good thing to ask about.
When I asked questions of potential therapists, I tried to keep the questions as open as possible, so they could answer from their own views and experience. (An example of a closed question, which they could answer with yes or no or not much more, is "Do you think you can help me?". An example of an open question, which allows them to answer more personally/fully and give you more of a sense of them, is "How do you think you might be able to help me" or "How do you think we might work together?".)
Maybe you could ask something like, "X has been a factor in my experiences. Have you got experience of working with clients who have experienced X?" or "How would you feel about working with someone with experiences relating to X?"
Something I'd say is that I don't think you need to have a right or wrong answer in mind for your questions. If you're making your questions open, it can be good to be open to a variety of answers. You'll know if what they say resonates or not.