A journalist may ask you to grant them an exclusive interview on a subject, which means that you cannot talk to another reporter about the same topic. This is normally done when they have the only relevant information or a good story, and it can be a powerful tool to increase their coverage in the press.
In an interview, it is often helpful to jot down questions ahead of time. However, it is also important to be flexible and to allow your conversation to prompt questions you had not previously considered. You want to sound natural and engaged, not like you are reading off an interview question list.
If a topic comes up that you are not comfortable discussing or you don’t know the answer to, be honest and respectful. It is better to be upfront than to give an answer that you don’t feel comfortable with and have your remarks misconstrued by the press. In this case, you can say that you would prefer not to comment on a particular topic, and that you will discuss it further when you are more prepared.