lat = 50.17, long = 6.03
The name of the small village 500 meter west of the tower of Buurgplaatz is Huldange.
Latitude: 50° 09' 42"
Longitude: 06° 01' 25"
The trouble I'm having with that is: Buurgplaatz is NOT Luxembourg's highest point. Go 1090 m south east and you will stand on Kneiff, exactly 1 m higher.
As Wolfgang wrote, the true high point of Luxembourg is Kneiff.
Why Buurgplaatz was believed to be the high point is explained very well in this article on the site of the Luxembourg topographical service.
Here's a picture of Kneiff: