How do I define a on focus Funktion?

Yes you can do this with ckeditor custom event :

CKEDITOR.instances.editor_name.document.on('focus', function(event) {
// your instructions
});

Hello,

where I have to place this?

I write this in my function.js

CKEDITOR.instances.dynContent1.document.on('focus', function(event) {
// your instructions
   alert('alert');
});

But the alert doesn't pop up when the instance get focus.

I tried also

CKEDITOR.add = function( editor ) {
   
   editor.on( 'focus', function(){
      alert('alert');
   });
};

In this way the function fire, but following function don' work.

function insertCK(editor, tag) {
   var oEditor = CKEDITOR.instances[editor];
   oEditor.insertHtml(tag);
}

Without CKEDITOR.add insertCK() works fine.

How can I reach, that both works (onfocus and inserCK())?

Thanks

Ngar

[edit]
I have to insert

CKEDITOR.instances[ editor.name ] = editor;

in the CKEDITOR.add-function.
[/edit]