The interviewer may ask this question to ensure that you are familiar with standard BA documents and how to apply them to a client's case. Even if they do not directly ask about your past experience here, providing examples can validate your ability to bring value to the employer.
Two diagrams I prefer using are Activity Diagrams and Use Case Diagrams. Activity Diagrams show the diverse activities that take place across various departments. I use Activity Diagrams to show who interacts with a system as well as the primary goals they achieve with it. I find Use Case Diagrams to be very useful when I need to visualize the functional requirements of a given system so I can make smart choices when it comes to design and figuring out development priorities.