Hey Sabrina and Brenda,
I moved this question to our monitored public space for better visibility. For your instance, you actually are using our Jive Rewards system (not Advanced Gamification) which has directions under Rewards .
Challenge a user is something you can do within the leaderboards to those who are similarly ranked. The most detail we have is when this feature was released in Rewards - 2016.2 Deep Dive. Is that what you are looking for (at the bottom of the blog post)?
Technical Account Manager