How do I determine what Siri commands an app supports? When an app supports Siri commands natively, how can I figure out what commands they support?

Note that this is asking specifically about app developer-defined commands built into the app. This is not asking about Siri Shortcuts in Settings, Siri Shortcuts you can define to an aspect of an app, nor a Siri command you can bind to a Shortcut in Shortcuts.app

Some apps have static built-in commands, for example, if you view Overcast’s App Store page and scroll down to the bottom, you’ll see it “Supports Siri and Family Sharing”. That Siri support badge is stating it supports Siri commands external to the app. “Hey Siri, play The Talk Show on Overcast”

How can I find out what Siri commands are natively supported by an app?
Invoke Siri, but don't ask her a question; instead, tap on the waveform so that she 
stops listening and shows you suggested questions. 
Next, scroll down to the app you're interested in and tap on it to see possible voice commands.