It's a one-page CS file embedded in the NodeXLApi.chm help file. Do this:
1. Find the help file. It was included in the NodeXL Class Libraries zip file that you downloaded.
2. Right-click the file in Windows Explorer and select Properties from the right-click menu.
3. In the NodeXLApi.chm Properties dialog box, click the "Unblock" button, if there is such a button. If you don't do this, you won't be able to view the help file's contents.
4. Open the NodeXLApi.chm help file and search for the "NodeXLControl Class" topic.
5. In that topic, search for the "Using NodeXLControl in WPF Applications" heading.