Get current GPS Constellation setting from an IQ App?

No, but you can set the constellations used Starting with CIQ 3.2.0.

https://developer.garmin.com/connect-iq/api-docs/Toybox/Position.html#enableLocationEvents-instance_function

Thanks Jim. That documentation states "If not provided, CONSTELLATION_GPS will be used by default". So does that mean that the global watch settings are ignored by the App? Do I need to code my own user interface to allow the user to set this option?

That's what I do.  Allow the user to set what they want.

There really isn't a global setting for this as you set it per activity, so CIQ apps are the same.