Is hearing constant repetition -- of questions, stories, inane comments -- grinding your patience to fine powder? We know you know it's the dementia doing the talking. But that doesn't make it much easier to deal with. What does: Changing something about the situation (or its trigger) to jar the person to a new topic.
What you can try:
Change the scenery. Go to another room. Sit in different chairs. This could take a particular object triggering a memory out of the person's line of vision, for example.
Change the topic. Try posing a question yourself or picking a topic you know to be a favorite, such as something from childhood, the local ball club, food.
Change the activity. Play music, have a snack, take a walk, offer a card game or puzzle.