Hallo,
I figured it out mayself.
GeometryEngine.Project is doing the job
The GPS coordinates for Parque Jose Marin in Cinefuegos has
a lattitude of -80.4531737 and a longitude of 22.1459153.
The GPS MapPoint is new MapPoint(-80.4531737, 22.1459153, SpatialReferences.Wgs84)
The GPS location is converted using GeometryEngine.Project
MapPoint mapped = GeometryEngine.Project(location, SpatialReferences.WebMercator) as MapPoint;
The mapped point can be used to create a marker and to set the position.
greetings
Clemens Hoffmann