Interview and Intellectual Property

I was asked some questions regarding my previous work experience at a competing firm during an interview. They asked me a few specific things (eg. what were your findings when you did xyz etcetc?) which made me feel uncomfortable because i) I dont remember the exact details and more importantly ii) i wasnt sure if revealing company A's work to company B is legal.

If I did research for company xyz and got paid, who does it belong to?

In the future interviews, should I just say "i cant tell you, the work belong to company xyz"?

What if the research was based on public information/data?

Thanks in advance