how to get recent registered author id?

I don’t think you need any SQL queries.

<?php

$args = array(
    'role'         => 'author', // authors only
    'orderby'      => 'registered', // registered date
    'order'        => 'DESC', // last registered goes first
    'number'       => 1 // limit to the last one, not required
);

$users = get_users( $args );

$last_user_registered = $users[0]; // the first user from the list

echo $last_user_registered->ID; // print user ID

Here you can find complete information on how to use get_users() function.