eg: you can do current.assigned_to.department.name to get the department name of the current assigned_to person on an incident form.

In the same way you can replicate your scenario:

var reqDetails = new GlideRecord('sc_req_item');  

//var catItem = reqDetails.addJoinQuery('sc_cat_item');  

reqDetails.addQuery('number',"RITM0000016");  

//catItem.addCondition('name', 'Hardware Exception Appeal');  

reqDetails.query();

reqDetails.next();

gs.addInfoMessage(reqDetails.cat_item.name);           // This will print the catalog item name

gs.addInfoMessage(reqDetails.cat_item.vendor.name); // this will print out the vendor name which is on the catalog item

Please mark the answer helpful or correct if you fell so.

Kind regards,

Sourabh