The XaaS blueprint will just trigger the workflow in vRO. I normally just keep the vRO Client open and watch the log stream for the workflow invocation. Once you have the client open you examine the data passed to the workflow by looking at the Variables tab under the invocation.
To list these via the workflow you can do like the below
In the green box, I'm storing the workflow inputs into a Properties map. These are the defined inputs for the workflow and in the XaaS form they will be listed as fields at all times.
In the red box, I'm then adding any extra parameters passed by the XaaS to the same map. These will include things passed by vRA (e.g., __asd_requestor, etc) as well as any additional fields I've added to the XaaS form. Additional fields need not be declared as inputs in the workflow but if they exist in the form they will be passed along to the invocation as context parameters.