sort.php

<?php
function products_query( $query )
{
  if ( ! $query->is_main_query() || is_admin() )
  {
    return $query;
  }

  if ( is_post_type_archive( 'product' ) || is_tax())
  {

    if (!isset($_GET['sort']) || empty($_GET['sort'])) {
        return;
    }

    // if sort a-z
    if ( $_GET['sort'] === 'a-z' )
    {
      $query->set('orderby', 'title');
      $query->set('order', 'ASC');
    }

    // if sort z-a
    if ( $_GET['sort'] === 'z-a' )
    {
      $query->set('orderby', 'title');
      $query->set('order', 'DESC');
    }

    // if sort lastest
    if ( $_GET['sort'] === 'latest' )
    {
      $query->set('orderby', 'date');
      $query->set('order', 'DESC');
    }
  }
}
add_action('pre_get_posts', 'tg_products_query');