Ponder allows you to create a micro-response on any document you can browse to, but it only shows the color-coded underlining on documents that are on one of your class reading lists or course packets.
(This is for privacy reasons.)
If you click on an existing response in your activity feed to access the document, Ponder will pull-down and render the response(s) there as well. However, it will not count reading on that document until it has been added to the reading list or course packet.
If you want the underlining to appear without clicking from the feed, you need the administrator of one of your groups (probably your teacher) to add the site or document to your course packet.
Or, you can create your own Ponder group and add it yourself.