Hello!
I would really appreciate some help with the finding of a technical term for doing qualitative interviews, but not with the person that has first-hand experience with something, but a secondary (expert) source. So for example, if instead of talking to person that suffered trauma about PTSD experience, I speak to a psychologist or counselor that has a lot of experience with this topic and has seen a lot of people and can summarise and give an insight of different perspectives from an expert angle.

If you know of articles using this approach, I would be really grateful if you could share them as well!
Thank you very much!

I'm not sure if you need a technical term to find this kind of research. In my literature searches for my field, I've come across papers based on interviews with professionals who work with people - I think if you just vary your search terms, you should find them.

They are called expert interviews. Try a Google search of 'expert interviews in research. Best of luck