The playerLoggedOut event does not add any new Properties. Since it is a MCPlayerEvent, you can already access the getter

This class was added by a mod with mod-id crafttweaker. So you need to have this mod installed if you want to use this feature.

Importing the class

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import at the very top of the file.

import crafttweaker.api.event.entity.player.MCPlayerLoggedOutEvent;

Extending MCPlayerEvent

MCPlayerLoggedOutEvent extends MCPlayerEvent. That means all methods available in MCPlayerEvent are also available in MCPlayerLoggedOutEvent