Open-ended questions begin with What, Why and How. They indicate the person is thinking and might elaborate a point. In the 1960s David Attenborough visited Australian aborigines. While you want to remain open, as Attenborough did, you also want to focus the conversation. Then again, you can submit an article to Cat Fancy and another version to ByLine .
Some authors advise against taking notes in the presence of interviewees.
Others, like me, must take notes during the interview. Your preferred note-taking method depends on your memory retention. I was in a glitzy restaurant interviewing a glamorous rising star. But, clever me, I taped the interview, freeing my hands to twirl pasta. Later I listened to the taped interview.