You do not want to interupt a narration. The child will then loose thier train of thought. The point of the narration is for the child to develope thier own relationship with the work. The things they remember and make connections with may be different then what you had in mind. If there is some information you want them to remember as well start by asking an open ended question about the topic, then discuss it.
No, I would ask open ended questions about it. I might have to give a few prompts, but usually once I say “tell me about____” my ds will usually be able to fill in the rest. When we first started narrating he would occasionally get hung up on one point in the story and it took some time to teach him that the had to pay attention to the whole story and tell me about it. If he couldn’t tell me anything about a part of a story except whatever he was thinking about, I would put the book aside, and when we should have been done with school work, I would pull it out again and read the section again and request another narration. It took a while but he did eventually get the idea that unless he wanted to do it again he had to listen to everything the first time.