There is no such single event. You can use the key event as well as afterCommandExec, but this one just states that a command has been executed, not that the content has changed. Also you'll need to listen to Paste and I'm not sure if drag&drop is covered by that.
I added the listener using the code below (content is my editor's name). All action you suggested work well except the drag and drop one. Since I dont know the name of the event, I tried "drop", "dragdrop" but both dont work. What is the event name for drag and drop?
Re: Does CKEditor has data changed event?
Re: Does CKEditor has data changed event?
CKEDITOR.instances.content.on("dragdrop",myFunction);
Re: Does CKEditor has data changed event?