Easiest way to add popup dialog with snippet of html/text using a wysiwyg editor?
Here is a recipe for that:


CKEditor Link: Used for linking to other content in your Drupal. In this case, I would create another Content-Type, e.g. Popup Snippet or sth similar. This is an optional component, depending on your exact requirements.
Colorbox Node: Used for presenting node content in a popup, stripped of the surrounding regions and other theme elements. It also provides an easy way to turn links into popups, by providing a 'magic' class, colorbox-node. This is the main component, and the main idea, allowing the user to 'popify' links by adding a class name to the link's properties in CKEditor.


Below are some screenshot of the result on a D7.  

Linking to content
  

Setting the colorbox-node class
  

End-result
  

Good luck!