STPointOnSurface (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns an arbitrary point located within the interior of a geometry instance.
Syntax
.STPointOnSurface ( )
Return Types
SQL Server return type: geometry
CLR return type: SqlGeometry
Open Geospatial Consortium (OGC) type: Point
Remarks
This method returns null if the instance is empty.
Examples
The following example creates a Polygon instance and uses STPointOnSurface() to find a point on the instance.
DECLARE @g geometry;
SET @g = geometry::STGeomFromText('POLYGON((0 0, 3 0, 3 3, 0 3, 0 0),(2 2, 2 1, 1 1, 1 2, 2 2))', 0);
SELECT @g.STPointOnSurface().ToString();