If you want to override the default- and the title ordering, and order instead by the last word in the title.
/**
* Override default- and title ordering in the backend, for the 'speaker' custom post type.
*
* @link https://wordpress.stackexchange.com/a/202154/26350
*/
add_action( 'pre_get_posts', function( \WP_Query $q )
{
if (
is_admin()
&& $q->is_main_query()
&& 'edit-speaker' === get_current_screen()->id
&& ( '' === $q->get( 'orderby' ) || 'title' === $q->get( 'orderby' ) )
) {
$q->set( 'orderby', 'wpse_last_word' );
$q->set( 'order', '' !== $q->get( 'order' ) ? $q->get( 'order' ) : 'ASC' );
}
} );
where we use the plugin from our last answer to support the wpse_last_word
ordering.