1. What is the name of the file whose snippet you copy/pasted in your latest response? The _NOT_AUTH that appears in the snippet appears to be a predefined constant; however, I was unable to locate it.

administrator/components/com_groupjive/admin.groupjive.php

2. Is there any documentation available for GJ?

For GJ 1.8, no. There will be for GJ 2.0 when released.

The documentation would have come in handy.

We didn't not make GJ 1.8. We fixed it so users had a group solution until we developed our own. GJ 1.8 is end-of-life.

1. Where do I get to see the forum, and also how do I use it?

You need Kunena 1.5.x, Kunena 1.6.x probably won't work with it. Once installed see backend configuration for GroupJive.

2. Where do I get to see the bulletinboard, and how to make use of it?

Navigate to a group and see its menu to browse/post on the bulletin board.

3. Whenever a registered user logs in, I would like them to know which groups they have been assigned to. I would also like this information to appear in the CB's user list, in one of the columns. How to make this possible?

GJ doesn't provide this. It's a standalone extension and there's not much relation to CB aside from the usage of its API to make it functional.

You'd need a custom fieldtype plugin to create a new field to keep track of users groups. You could also use documentation subscriber incubator project CB Query Field to create a field that displays results of a database query. This means you could query GJs database table and return a users groups, etc...

4. What are the various functions and features that the JG further makes possible for me?

You'll need to explore GJ for this. It's very basic and strictly provides groups for users in nested categories.. that's about it.

In the front-end, how do I get the bulletinboard to appear and be used?

You need to navigate to a group and you can use its bulletin from there. Please check that it is enabled within GJ configuration.