public enum WktFormatMode : System.Enum, System.IComparable, System.IConvertible, System.IFormattable  

SpatialReference sr = SpatialReferences.WebMercator;

// Get Esri WKT
string wkt = sr.Wkt;
/*
  PROJCS["WGS_1984_Web_Mercator_Auxiliary_Sphere",
   GEOGCS["GCS_WGS_1984",
    DATUM["D_WGS_1984",
     SPHEROID["WGS_1984", 6378137.0, 298.257223563]],
    PRIMEM["Greenwich", 0.0],
    UNIT["Degree", 0.0174532925199433]],
   PROJECTION["Mercator_Auxiliary_Sphere"],
   PARAMETER["False_Easting", 0.0],
   PARAMETER["False_Northing", 0.0],
   PARAMETER["Central_Meridian", 0.0],
   PARAMETER["Standard_Parallel_1", 0.0],
   PARAMETER["Auxiliary_Sphere_Type", 0.0],
   UNIT["Meter", 1.0]]
*/

// Get OGC WKT2
string wkt2 = sr.GetWkt2(WktFormatMode.None);
/*
  PROJCRS["WGS_1984_Web_Mercator_Auxiliary_Sphere",
   BASEGEOGCRS["GCS_WGS_1984",
    DYNAMIC[FRAMEEPOCH[1990.5], MODEL["AM0-2"]],
    DATUM["D_WGS_1984",
     ELLIPSOID["WGS_1984", 6378137.0, 298.257223563, LENGTHUNIT["Meter", 1.0]]],
    PRIMEM["Greenwich", 0.0, ANGLEUNIT["Degree", 0.0174532925199433]],
    CS[ellipsoidal, 2],
    AXIS["Latitude (lat)", north, ORDER[1]],
    AXIS["Longitude (lon)", east, ORDER[2]],
    ANGLEUNIT["Degree", 0.0174532925199433]],
   CONVERSION["Mercator_Auxiliary_Sphere",
    METHOD["Mercator_Auxiliary_Sphere"],
    PARAMETER["False_Easting", 0.0, LENGTHUNIT["Meter", 1.0]],
    PARAMETER["False_Northing", 0.0, LENGTHUNIT["Meter", 1.0]],
    PARAMETER["Central_Meridian", 0.0, ANGLEUNIT["Degree", 0.0174532925199433]],
    PARAMETER["Standard_Parallel_1", 0.0, ANGLEUNIT["Degree", 0.0174532925199433]],
    PARAMETER["Auxiliary_Sphere_Type", 0.0]],
   CS[Cartesian, 2],
   AXIS["Easting (X)", east, ORDER[1]],
   AXIS["Northing (Y)", north, ORDER[2]],
   LENGTHUNIT["Meter", 1.0]]
*/

// You can create a spatial reference with the Esri WKT string or the OCG WKT2 string
sr = SpatialReferenceBuilder.CreateSpatialReference(wkt2);

// Get OGC WKT2 including authority in top-level objects
// In this case the authority is written as ID["EPSG",3857]
wkt2 = sr.GetWkt2(WktFormatMode.AuthorityTop);
/*  
  PROJCRS["WGS_1984_Web_Mercator_Auxiliary_Sphere",
   BASEGEOGCRS["GCS_WGS_1984",
   DYNAMIC[FRAMEEPOCH[1990.5],MODEL["AM0-2"]],
   DATUM["D_WGS_1984",
    ELLIPSOID["WGS_1984",6378137.0,298.257223563,LENGTHUNIT["Meter",1.0]]],
   PRIMEM["Greenwich",0.0,ANGLEUNIT["Degree",0.017453292519943295]],
   CS[ellipsoidal,2],
   AXIS["Latitude (lat)",north,ORDER[1]],
   AXIS["Longitude(lon)",east,ORDER[2]],
   ANGLEUNIT["Degree",0.017453292519943295]],
   CONVERSION["Mercator_Auxiliary_Sphere",
    METHOD["Mercator_Auxiliary_Sphere"],
    PARAMETER["False_Easting",0.0,LENGTHUNIT["Meter",1.0]],
    PARAMETER["False_Northing",0.0,LENGTHUNIT["Meter",1.0]],
    PARAMETER["Central_Meridian",0.0,ANGLEUNIT["Degree",0.017453292519943295]],
    PARAMETER["Standard_Parallel_1",0.0,ANGLEUNIT["Degree",0.017453292519943295]],
    PARAMETER["Auxiliary_Sphere_Type",0.0]],
    CS[Cartesian,2],
    AXIS["Easting (X)",east,ORDER[1]],
    AXIS["Northing (Y)",north,ORDER[2]],
    LENGTHUNIT["Meter",1.0],
    ID["EPSG",3857]]
*/

// Get OGC WKT2 including authority in all objects
// Authority is written as ID["ESPG",<id>] or ID["Esri",<id>]
wkt2 = sr.GetWkt2(WktFormatMode.AuthorityAll);
/*
  PROJCRS["WGS_1984_Web_Mercator_Auxiliary_Sphere",
   BASEGEOGCRS["GCS_WGS_1984",
    DYNAMIC[FRAMEEPOCH[1990.5],MODEL["AM0-2"]],
    DATUM["D_WGS_1984",
     ELLIPSOID["WGS_1984",6378137.0,298.257223563,LENGTHUNIT["Meter",1.0,ID["EPSG",9001]],ID["EPSG",7030]],
     ID["EPSG",6326]],
    PRIMEM["Greenwich",0.0,ANGLEUNIT["Degree",0.017453292519943295,ID["EPSG",9102]],ID["EPSG",8901]],
    CS[ellipsoidal,2],
    AXIS["Latitude (lat)",north,ORDER[1]],
    AXIS["Longitude(lon)",east,ORDER[2]],
    ANGLEUNIT["Degree",0.017453292519943295,ID["EPSG",9102]],ID["EPSG",4326]],
    CONVERSION["Mercator_Auxiliary_Sphere",
     METHOD["Mercator_Auxiliary_Sphere",ID["Esri",43104]],
     PARAMETER["False_Easting",0.0,LENGTHUNIT["Meter",1.0,ID["EPSG",9001]],ID["Esri",100001]],
     PARAMETER["False_Northing",0.0,LENGTHUNIT["Meter",1.0,ID["EPSG",9001]],ID["Esri",100002]],
     PARAMETER["Central_Meridian",0.0,ANGLEUNIT["Degree",0.017453292519943295,ID["EPSG",9102]],ID["Esri",100010]],
     PARAMETER["Standard_Parallel_1",0.0,ANGLEUNIT["Degree",0.017453292519943295,ID["EPSG",9102]],ID["Esri",100025]],
     PARAMETER["Auxiliary_Sphere_Type",0.0,ID["Esri",100035]]],
    CS[Cartesian,2],
    AXIS["Easting(X)",east,ORDER[1]],
    AXIS["Northing (Y)",north,ORDER[2]],
    LENGTHUNIT["Meter",1.0,ID["EPSG",9001]],
    ID["EPSG",3857]]
*/