public bool Snappable {get; set;}

var featureLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>().FirstOrDefault();
// is the layer snappable?
bool isSnappable = featureLayer.IsSnappable;
// set snappability for a specific layer - needs to run on the MCT
await QueuedTask.Run(() =>
{
  // use an extension method
  featureLayer.SetSnappable(true);

  // or use the CIM directly
  //var layerDef = fLayer.GetDefinition() as ArcGIS.Core.CIM.CIMGeoFeatureLayerBase;
  //layerDef.Snappable = true;
  //fLayer.SetDefinition(layerDef);
});
// turn all layers snappability off
var layerList = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>();
await QueuedTask.Run(() =>
{
  foreach (var layer in layerList)
  {
    layer.SetSnappable(false);
  }
});