An Update from a previous post:

Some users are reporting that some of their recent activity is no longer showing up, like comments on other friends’ posts or event activity on Facebook’s new Timeline. It appears Facebook has now removed the option to display such stories at all on Timeline. From now on, stories such as commenting activity and event invites will appear in the News Feed and Ticker based on your friends’ subscriptions to you and your subscription to theirs. There seems to be a glitch with Event Activity that has yet to be fixed for users who have hidden it in the past and are now unable to unhide it. 

For example, if you go to a friend’s Timeline, you will not be able to see whose posts they have commented on recently. If you want to find out, you would have to go to Subscribed (at the top) and check “Comments and Likes.” From then on, whenever that friend likes or comments on something, it will appear in the Ticker (above the chat bar on the right side).

It does not look like Facebook will ever restore commenting/event activity to Timeline.