I know you have already accepted an answer, but i think this will help you.
You can first generate the code for Facebook Comments here.
For each page that you implement the comments plugin in, you'll be providing a href of the page the user is reading/visiting, as it is required by the plugin.
You can use the Javascript SDK to listen to Facebook events, for comments specifically you have the comment.create event, which is fired every time a comment is made. This event passes a response object to its callback function, which contains the href mentioned previously, and the commentID of the comment just generated. Hence you can easily track which page(url) a user has commented on.
Example (see how we can listen to the comment.create event):
<div id="fb-root"></div>
<script>
window.fbAsyncInit = function() {
FB.init({
appId : 'YOUR_APP_ID', // App ID
channelUrl : '//WWW.YOUR_DOMAIN.COM/channel.html', // Channel File
status : true, // check login status
cookie : true, // enable cookies to allow the server to access the session
xfbml : true // parse XFBML
});
// Additional initialization code here, this is where we listen to events
FB.Event.subscribe('comment.create',
function(response) {
alert('You commented on the URL: ' + response.href + 'CommentID: ' + response.commentID);
// do an ajax call to server to store user,commentID,href info if you require
}
);
};
// Load the SDK Asynchronously
(function(d){
var js, id = 'facebook-jssdk', ref = d.getElementsByTagName('script')[0];
if (d.getElementById(id)) {return;}
js = d.createElement('script'); js.id = id; js.async = true;
js.src = "//connect.facebook.net/en_US/all.js";
ref.parentNode.insertBefore(js, ref);
}(document));
</script>