Myndbend Article Wizard offers great ways to quickly see what is requester subscribed to, to subscribe/unsubscribe him from additional resources, and to see who else is subscribed to a particular article.
These are great recourses for pointing your users in the right direction, as well as to know what they already covered in your Knowledgebase.
See what articles are requester subscribed to
You can see what articles are requester subscribed to directly in the sidebar of your ticket:
Search for additional articles and subscribe the user to them:
Unsubscribe users from articles they are subscribed to: