Take a look at the "CB Activity - Comment" and similar system actions to get started with that. There isn't a trigger specific to GJ in CB Activity. You will need to do conditions against asset/source to determine if the comment is on group activity.

You can configure a JSON output under the Output tab, but you won't have access to the newly created group from there. There's a feature pending to allow support for that (passing newly created data to substitutions) and will review implementing that now as the other other way is to use a PHP output and write the necessary PHP to get the newly created group object.

forge.joomlapolis.com/issues/8847

Ok, latest CB Auto Actions build release available now supports Action Data. This is data added to substitutions and PHP based rendering from auto actions themselves. In the case of CB GroupJive when creating a new group the new group object will be in the action data. An explanation of substitutions usage (including action data) has been added to the Parameters tab of auto actions. Example of how to use this as follows.

1. Create auto action that creates a GJ group
2. Configure Output to JSON
3. Supply the following as the Layout4. Set method to PHP

Now run your auto action and it should respond with the JSON structure for that group object. You can use this behavior to completely customize the JSON response to whatever you need.

The new action data feature is supposed in over a dozen action types. Primarily in those that create new objects.