No, DT does not show known topics. What do you want to do with it? Are you looking for a scholar with a specific knowledge? Or do you want to see an overview for a given dwarf? If it is just for researching about research, it may be better to use DFHack.
1. I'm getting visitors who want to join as scholars. If they know about topics that my scholars don't know about, then I definitely want them.
2. If I take those new scholars, then I want to watch that new knowledge spread to the other scholars through discussion and apprenticeship.
3. If my scholars have lots of topic knowledge that isn't represented in books, then I could put them into a no-book library that will make them write a little faster.
4. Suppose I'm considering getting books from outside, whether buying, stealing, or conquering. In making that decision, it would be nice to know whether the books I'm thinking of acquiring have knowledge of topics that my scholars lack.
5. When I acquire books with outside knowledge, then I want to watch that knowledge spread through my scholars as they read the new books and discuss those topics.
6. If I run a library-focused fortress for several years, then I want to watch my scholars become super-knowledgeable. And I want to see if the knowledge tracks their skills and interests. Will the doctors stick to medical topics, or will they branch out into math or philosophy? Will the legendary mechanic study engineering, or will he be drawn to history?
Patrik's librarian script is a crucial tool for those of us who want to collect all the topics. But it only addresses books, which are half the picture. I was hoping that DT could fill in the other half.
Edit: Just now I watched a watched a grand master chemist write about liquid-liquid extraction. It's the first book on that topic in my fortress. I assume that the other scholars will read it and advance their own knowledge, but right now there's no way for me to tell.