I get this popup on my Macbook Pro High Sierra 10.13.6.
There is no title bar. When I click on the popup it does not become selected and the "current application" in the Mac menu remains whatever it was.
How can I tell what application is displaying this popup? How can I tell what it means? What is a "location" -- is this a GPS thing, a network thing (wifi? Bluetooth?), is it from Maps? Has my Mac discovered new unknown lands and expanded the horizons of mankind? How am I supposed to know? What if I Add? What if I Decline? What happens in either case? Am I like Kyle in Human Centipad?