Years ago when I started my genealogy research, I would occasionally give my grandparents various records I had located on their grandparents or great-grandparents. My maternal grandparents had a moderate interest in genealogy and I enjoyed sharing my discoveries with them.
After these grandparents passed, I ended up with most of their papers–including the copies I had made for them years ago of various records. I didn’t need the duplicate copies of things. But what was helpful was the notes that my grandma had written on some of them. Many of these details were things that I did not know.
If you are needing a memory prompt, consider giving that relative copies of a few family documents. Encourage them to write on them and mark them up. Their comments may contain details of which you are unaware. Information on a record could easily be the trigger to pull memories out of the depths of their mind.