Say a product name in a different list?
Can you detail your need?
As far as I understand and if you're talking about a Nintex List Form, I think that you should better use a workflow starting when the item is created and/or modified to update an item in a different list.
here http://vadimtabakman.com/nintex-forms-starting-a-workflow-and-waiting.aspx Vadim published an example how to start workflow from form's script.
so you might get inspired and adapt it to update list items.
Retrieving data ...