How to display a specific field instead of Title with Entity Reference
If you edit your entity reference field you'll see an "Entity Selection" fieldset section. There is a "Mode" field in there that defaults to "Simple" which just lists the entity titles.  You can change that to "Views" which lets you use a custom View to display the selection.

You'll want to create a View first. Just create the View to display the fields you want.  That could be the Cours Title and CoursRefNumber if you want.