There is no reference to a real-world elevation datum in SU.
The geographic coordinates of a geo-located model coincide with SketchUp’s Origin [0,0,0]
The elevation of the terrain at those geographic coordinates also coincides with SketchUp’s Origin.
However, if you have knowledge of the real-world elevation at the model coordinates, then one of @TIG’s plugins may be of interest.
TIG: Add Height from Datum v2.0
TIG: Coords-Tag from Datum v3.4
FAQ for Add Location changes in SketchUp
https://help.sketchup.com/en/geodatachange