//check if any ckeditor instance has focus
if(CKEDITOR.currentInstance)
  console.log('editor has focus!');

//adding on focus handler
CKEDITOR.instances.ckeditor.on('focus', function(){
   console.log('focus')
});

tested with CKEDITOR 3.0 and Firefox 3.6.12 and IE 8

tracking focus in CKEDITOR

javascript

JavaScript