Sorry for the delayed response @Clint_Dovholuk!
Using slash commands, I think you can watch all categories like this:
/discourse watch
But the easiest way to configure notification rules is from the Discourse admin panel. There, all the options are clearly displayed in the UI, so there’s no need to try and work out the precise ‘slash command’ syntax. Check out the ‘configuring rules’ section of the plugin’s documentation for more info.