Modify wp_title for custom post types using custom fields data?

The filter wp_title won’t pass $id to your function. Drop the parameter and instead retrieve it with get_queried_object_id():

function dw_listing_title( $title ) {
    if ( is_singular() && $id = get_queried_object_id() ) {
       // Modify $title as required
    }

    return $title;
}