Display last query using ?show_query=true

functions.php

<?php
/*******************************************************************
 * as seen on - https://www.youtube.com/watch?v=oWXjVUcPSPk
 * by: Tom McFarlin
 ********************/
add_filter( 'posts_request', 'my_show_query' );
function my_show_query( $query ){
  
  if ( isset( $_GET['show_query'] ) && 'true' === $_GET['show_query'] ) {
    var_dump( $query );
  }
  
  return $query;
  
}