I hope this question is not too subjective (as I was told while composing the question).
This question might appear to be an odd one, I suppose. So some background info: I recently had a phone interview for a researcher position. The interviewer was not an HR person but the person who I would actually work for, if I were hired. I got the interview because my friend forwarded my resume to someone within the company that he knew.
While I know the general things that the company does, I do not know anything specific. Digging online did not give me any useful info, because none of the job openings posted online seemed remotely related to my expertise.
During the phone interviewer, the interviewer asked me questions about my background. I also asked him about the specific responsibilities of this position he was trying to fill. His response was a really vague and general, and he said that based on my resume, I could potentially offer something more than the other people whose resumes he had read.
Towards the end of the phone call, he said he would invite me for an onsite interview.
Now I haven't been contacted about the onsite interview yet (the phone interview happened less than a week ago), but I am curious as to how I can even prepare for this kind of interview given the lack of information.