Events documentation for Craft 3
Whilst Doug's answer is useful for knowing the ins and outs of a particular event once you've found it, actually finding which events are available in Craft 3 in the current docs is not straight-forward. After a bit of digging, you'll find that most events are part of Craft's services - so head to the Class Reference and choose the most relevant service from the craft/services menu. The events available to each service are listed at the end. For example: https://docs.craftcms.com/api/v3/craft-services-users.html#events