You can set up events to trigger off any link that is clicked and/or visited. When you go to set up a quest choose the Custom Event option and you can choose if it's triggered by the user manually checking the event as completed, by the user clicking on a link, or by getting an event completion API from an external source (in this case the Event RSVP, if possible. For the last option you can check out the documentation here: https://docs.jivesoftware.com/cloud_int/comm_mgr/jive.help.rewards/#admin/RewardingActivityfromOtherSystems.html
The event completion by user clicking on a link may be the easiest one for you to implement. It doesn't take into account that the user actually RSVPs for the event (though tthere may be a separate destination link for that which you can key off of) but it will get you part of the way there.
Hope that helps.