The option to copy and paste widgets has been added with K13 Refresh 2 (13.0.31).
And a bug related to copying widgets with widget zone restrictions has been fixed with Refresh 6 (13.0.73).
If you hover over a widget in the page builder, you should see the copy icon at the top right. If not, do you have any errors in the browser console log and/or Kentico event log? And what is your hotfix version?