I have been looking for this too- I have a category for Spanish language discussions and my facilitator is curious about who is reading content.
The only way to find out which reports have filters fo category is to click through them all - so far I have found the ones with this feature include:
- Posts
- Post Edits
- Bookmarks
- Likes
e.g. all the things users do to interact with a post. I cannot find anything that lets me understand traffic within a category