That's the legacy plugin library files location. We used to copy a plugins library files to that location, but it's not necessary to do that anymore. You'll find that file at its original location below.
/components/com_comprofiler/plugin/user/plug_cbgroupjive/library/Table/GroupTable.php
You shouldn't need to modify it through. You can store custom fields into the "params" column automatically. This will avoid having to modify core code. When using CB Auto Actions to output your custom field just be sure its scoped to params. Example as follows.
FROM:
Code:
<input type="text" name="gj_custom" class="form-control" />
TO:
Code:
<input type="text" name="params[gj_custom]" class="form-control" />
You can then access it using the below.
Code:
$myCustomValue = $row->params()->get( 'gj_custom' );
The gj_onBeforeDisplayGroupEdit trigger can be used to add the custom fields with params scope.