It'll only work if you're using a comment fieldtype using the below usage. It's not possible for CB Auto Actions to do this for the activity stream comments as the comment is linked to the activity entry and not the activity entry user.

Global
Triggers: activity_onPushComments
Type: Email
User: Automatic
Access: Everybody
Conditionals
1: [var2_type] Equal To field
2: [var2_parent] Equal To MODERATOR_USER_ID_HERE
Action
To: Email address of the moderator here

In short you need an auto action per moderator with their id conditioned against and their email address manually added.

Is there any complete list of variables "var2_type", "var2_message" or something like "var2_userid", where I can get all infos about these vars?

Every database column in _comprofiler_plugin_activity_comments is available. var2 is the comment database object.

CB Activity doesn't know the comment recipient is a user. It's generic in the sense it uses a pathing system of type, subtype, item, and parent columns to determine its source location. I doesn't know parent is specifically a CB user object so it doesn't build and send one with the trigger. I hope to eventually improve this when I deprecate those columns in favor of a single "asset" column then build additional objects off the asset as needed to allow the trigger to have more information. This is detailed a bit further below, but that's a bit of ways off as am working on CB Gallery at the moment.

forge.joomlapolis.com/issues/5825

thank you for your reply. So, its not possible for the CB-Activity comments directly?

When a comment is made on an activity entry the comment is linked to that activity entry. It's not linked to a specific user. This means there's no user id to check against to ensure they're commenting on a moderators activity post, which is why this would only for for a comment field at this time. It is possible to send a notification, but there's just nothing to check to ensure only moderators are notified.

Is there a chance of getting that function with CB-Notifications at some time?

Doesn't really have anything to do with CB Notifications. The trigger in CB Activity needs to provide more information and for it to be able to I need to rewrite/improve the stream object construction so it can construct objects based off the activity or comment type, subtype, item, and parent (soon to all be a single asset column). CB Notifications also probably won't be for a long time as I've other projects to work on at this time.