To search for ungrouped Trainees, on the Left Navigation click "Users". Next to the search box, click "Advanced Filters" link.
In the Advanced Filters popup window, select “Ungrouped” from the drop down menu next to the Groups section. Next, click Search.
Tip: You can add additional values as part of this search to find exactly the Trainees you need.
Now, You will now see a list of Trainees who are not a part of any Group.