CB Auto Actions attempts to automatically find the first valid user object or attempts to build one from discovered user ids. So [name] should already be the group event owners name.
The problem will be getting the group name since all an event contains is the group id and not the name. So you'll need to use format functions for that. Under the Parameters tab enable format functions. Then below that you should see all the available format functions. These will even let you run inline queries or custom PHP. Probably the easiest solution here is to use code since the event does contain a way to get the group object. Below should work.
Code:
[cb:parse function="code"]return $variables['var1']->group()->getString( 'name', '' );[/cb:parse]