Thanks again, endecotp. I really did appreciate your answer and hope I didn't seem ungrateful.
I think you are right and I might as well proceed with taking screenshots using my best judgement. I've already put the issue to Developer Support and they were really helpful, but weren't able to give me a definitive answer about what is expected when the "item or service" is a json file. To be fair, it was over the holiday weekend when they are not fully staffed. My support staffer did commit to using my case as a form of feedback to the App Review teams. Hopefully this will result in Apple making it more clear what they want to see in these screenshots. We also agreed that the Developer Forums would be a good alternative and I was pretty thrilled to get an answer here within 1 hour.
So I'll take your advice and not waste time waiting for Apple to "chime in" here.
Again, many thanks!