The Calls in Queue is displayed as a report within CAD. Agents would have to click on the Reports icon (or Ctrl-Q) then select Contact Service Queue Statistics.
If you want more detail, one workaround is to use a wallboard. There are some opensource ones available (search the forums). If you have a web-based wallboard setup, you can customize it, then display it as a tab within the CAD integrated browser. That way your agents always see it (without clicking), and you can show any data you want.
I don't believe you can modify the Supervisor Desktop icons.