See plugin , but it’s not a complete list. Plugin directory | Discourse - Civilized Discussion lists official plugins used on CDCK hosting. You can consider those safe. I install most of those on my installation packages. Though I do my best to see that the Discourse official Standard Installation instructions are clear, I’ve also spent several years automating installations for those who don’t want to deal with the unix command line.
Also, (other than the official plugins linked above) don’t go looking for plugins until you have a problem that you want to solve, otherwise, you’re asking for trouble. Some people think “I’ll install every plugin I can find to see what they do”. It never ends well.