I know this can be done with the On premisis Nintex, bot, since the O365 versions do not have the ability to create UDA, I wonder how this can be done using O365 Workflow. Possible?
You can get the Form Data XML in a workflow using the Item Reference NFFormData
Then traverse this data just similarly that you would on premise using Query XML.
There are a few examples linked below as well as the Xchange at Parsing Nintex Forms Repeating Section Solution - O365
Nintex Forms Repeater XML Format
Parsing Repeater XML
You can also connect the Repeating Section to a multi-line text field (plain text) in your list. Then just parse with Query XML.
That's correct Jason Durrant, and an example of that for those that want to use that option is in the link above.
Retrieving data ...