There are several posts here about using Nintex Workflow to get data from a Nintex Form repeating section. The trick is to create a list column of multi-line text and set your Repeating Section control's "Connected to" setting to that multi-line column, and Workflow can parse the XML output stored in that column.
Well, I noticed something different in the new responsive designer. Normally when you add a control into the repeating section, you can name the control and that name will be used in the XML output, so you can set your XPath query to //<controllname>.
In the new responsive designer, the XML output uses random numbers instead of the name you gave the control. Thus the XML looks like this,
<?xml version="1.0" encoding="utf-8"?><RepeaterData><Version>1.0</Version><Items><Item><_d1c6bb8c4ea50881a5b6e43e1e6ca973 type="System.String">user input here</_d1c6bb8c4ea50881a5b6e43e1e6ca973> etc
Therefore, to get the data I had to set my XPath query to
//_d1c6bb8c4ea50881a5b6e43e1e6ca973
Hope this helps someone.