Display trackbacks separately from comments in twentyeleven

Use the typeparam in the function wp_list_comments().
Copy the comments.php to your Child Theme. search for wp_list_comments. Find this:

    <ol class="commentlist">
        <?php
            /* Loop through and list the comments. Tell wp_list_comments()
             * to use twentyeleven_comment() to format the comments.
             * If you want to overload this in a child theme then you can
             * define twentyeleven_comment() and that will be used instead.
             * See twentyeleven_comment() in twentyeleven/functions.php for more.
             */
            wp_list_comments( array( 'callback' => 'twentyeleven_comment' ) );
        ?>
    </ol>

Change this with your Params, like this:

    <ol class="commentlist">
    <?php
        // only comments
        wp_list_comments( array( 'type' => 'comment', 'callback' => 'twentyeleven_comment' ) );

        // only pingbacks
        wp_list_comments( array( 'type' => 'pingback', 'callback' => 'twentyeleven_comment' ) );
    ?>
    </ol>

You can also use the param value pings, there have include trackback and pingback; maybe you will only show pingback, then use the value pingback for the valueparam. Also you can change the markup of html to more difference in the output.

If you will separate the pingback and comments in seperate areas, then like this.

<ol class="commentlist">
    <?php
        wp_list_comments( array( 'type' => 'comment', 'callback' => 'twentyeleven_comment' ) );
    ?>
</ol>
<ol class="pingbacklist">
    <?php
        wp_list_comments( array( 'type' => 'pingback', 'callback' => 'twentyeleven_comment' ) );
    ?>
</ol>

Now a screenshot of the results to the code above:

At last, the param typeand his possibilities:

$type – (string) (optional)

The type of comment(s) to display. Can be 'all', 'comment', 'trackback', 'pingback', or 'pings'. 'pings' is 'trackback' and 'pingback' together.

Default: 'all'