Hello,

You can use this below for Surveys.. you can customize as per your requirement this below link. 

template.print('<a href="https://' + gs.getProperty('instance_name') + '.service-now.com/nav_to.do?uri=incident.do?sys_id=' + gr.sys_id + '">' + gr.number + '</a>');

You have to do 2 things, first is the 

1. Create a new email script:

(function runMailScript(/* GlideRecord */ current, /* TemplatePrinter */ template,
/* Optional EmailOutbound */ email, /* Optional GlideRecord */ email_action,
/* Optional GlideRecord */ event) {

// Add your code here
var url= <<your portal url>>;
template.print('<a href=' + url + '>Portal link </a' );
})(current, template, email, email_action, event);

2. Go to the notification HTML message, add

Lights...Camera...Action! ${mail_script:<<name of the script you created in step>>} is coming soon!

${mail_script:<<name of the script you created in step>>} - responsible to show the url in the mail

Let me know if it helps.

Thanks,

Vaishnavi