I have just installed the KA JavaScript SDK plugin. It is configured and enabled. You should see the comments on this test page:
test.purepoint.nl/nieuwsblog/42-hygiene-als-hot-issue

However, the SDK code doesn't show up in the source and the comments are not displayed. When I add the Facebook plugin code (from developers.facebook.com) directly to index.php, the comments are displayed (but are not posted to facebook).

What am I doing wrong?

Post your plugin version and Joomla.

Also try to disable all other Facebook extension and test to check if there is any conflicts.

Regards