I have successfully got a functioning NodeJS/Express app situated in a properly functioning Frappe app.
The next step was to get going with…
frappe.publish_realtime('my_event', {etc})
… in the Frappe app and with …
var subscriber = redis.createClient();
subscriber.on("my_event", function (channel, message) { etc, etc })
… running in the NodeJS app.
I used this article to get started : How to get Realtime Updates in your App from ERPNext via Socket.io and Redis, but it has a bunch of errors, so I don’t think the author (@joshiparthin ?? ) ever tested to be sure he was describing something that functions as advertised.
Meanwhile, I can’t find any evidence in my system that publish_realtime() is actually doing anything at all.
I searched the code and found that chat and blog post both use subscriber.on, but in my development environment neither of those work. 
There are hints from several years ago that publish_realtime() only works in production mode.
There’s this Github Issue : [ frappe.async.realtime_publish not working] (frappe.async.realtime_publish not working · Issue #1963 · frappe/frappe · GitHub) and there’s this post : Frappe.publish_realtime
My questions are:
How can I see, with logging messages, or similar, if frappe.publish_realtime() is actually publishing my event?
Does publish_realtime() NOT work in development mode?