I think you also need to add a link to queryobj.php. The problem may also be that you're using an absolute reference to the Webassist files i.e. /webassist - it's my understanding that if you use absolute references in PHP code, it will refer to the root on the server and not the website, for example /var/www/vhosts/mydomain.com/httpdocs. Try making your file paths relative, i.e.
<?php require_once('../webassist/mysqli/queryobj.php'); ?>