STAsText (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns the Open Geospatial Consortium (OGC) Well-Known Text (WKT) representation of a geometry instance. This text will not contain any Z (elevation) or M (measure) values carried by the instance.
Syntax
.STAsText ( )
Return Types
SQL Server return type: nvarchar(max)
CLR return type: SqlChars
Examples
The following example creates a LineString geometry instance from (0,0) to (2,3) from text. STAsText() returns the result in text.
DECLARE @g geometry;
SET @g = geometry::STGeomFromText('LINESTRING(0 0, 2 3)', 0);
SELECT @g.STAsText();