While on the Friends List, click on the Challenges icon below their name to be taken to a page to see the Challenges that your Friend has set up and to see the details and their progress on each Challenge. If you do NOT see an icon under your Friend's name for Challenge, it means you do not have their permission to view them.
If you want to help keep your Friend on top of their chosen Challenges, look at the times when the Challenges take place and set up some Reminders and Notifications for them so you will be alerted when a reading has or has NOT taken place. Also, you can see if your Friend has set up one of the Challenges (indicated by a Medallion attached to it) as a Weekly Reward Challenge for Reward Medallions! For more details on a Challenge, simply click on it's icon and you will be able to see your Friend's progress for each Challenge.