BuddyPress.org

The

bp_get_group_id() will only work if you are on group page.

In case you are not on group page and want to know the group id, there is a way to find that, but you will have to know the group slug(check the url of group for slug)

$group_id=BP_Groups_Group::get_id_from_slug($slug);

where $slug is the group slug.