public static void SetSnapMode( 
   SnapMode mode,
   bool value
)

// set only Point and Edge snapping modes, clear everything else
Snapping.SetSnapModes(
  new List<SnapMode>() { SnapMode.Point, SnapMode.Edge });

// clear all snap modes
Snapping.SetSnapModes(null);

// set snap modes one at a time
Snapping.SetSnapMode(SnapMode.Edge, true);
Snapping.SetSnapMode(SnapMode.End, true);
Snapping.SetSnapMode(SnapMode.Intersection, true);

// get current snap modes
var snapModes = Snapping.SnapModes;

// get state of a specific snap mode
bool isOn = Snapping.GetSnapMode(SnapMode.Vertex);

// interested in only snapping to the vertices of a specific layer of interest and not the vertices of other layers
//  all other snapModes should be off.

// snapping must be on
Snapping.IsEnabled = true;

// turn all application snapModes off
Snapping.SetSnapModes(null);

// set application snapMode vertex on 
Snapping.SetSnapMode(SnapMode.Vertex, true);

// ensure layer snapping is on
await QueuedTask.Run(() =>
{
  featureLayer.SetSnappable(true);
});

// set vertex snapping only
var vertexOnly = new LayerSnapModes(false) { Vertex = true };

// set vertex only for the specific layer, clearing all others
var dict = new Dictionary<Layer, LayerSnapModes>();
dict.Add(featureLayer, vertexOnly);
Snapping.SetLayerSnapModes(dict, true);  // true = reset other layers