One of my dc's was like this. He also refused to answer the kind of emotional, open-ended questions that grade-school English (sorry, Language Arts) is full of: "How did the book make you feel?" "Have you ever been in the same situation?" "What's the schema for the book (meaning context/connections to real life)?" etc. Hated, hated, hated that stuff and didn't see the point. Me either. He was hugely relieved to progress to homeschool at age 9 and then to high-school English, both of which we run on a college model. He now loves analyzing text rather than emoting about it or summarizing it.
So, I sympathize with you and your ds. Do you think he might be willing to write about what he reads, e.g., a little book review blog or something? Picking up on Sweetie's idea, you could say, truthfully, it would be helpful to others to know what the book is about and what was good or bad about it. That would build some analytical thinking while also testing comprehension. He might even write or start some peer reviews for the local library -- our library will post (well-done) peer reviews near books. Just a thought.
If I had it all to do over again, I'd probably help my dc build analytical opinions supported by the text. Even at a young age, they and you together probably can tease out some reasons why a book is good or bad (you liked the narrator; why? you didn't think the characters were interesting; why? It was boring; why?).
