public SceneLayerDataSourceType GetDataSourceType()

//Must be called on the MCT
var dataSourceType = featSceneLayer?.GetDataSourceType() ?? 
                           SceneLayerDataSourceType.Unknown;
if (dataSourceType == SceneLayerDataSourceType.SLPK)
{
  //Uses SLPK - only cached attributes
}
else if (dataSourceType == SceneLayerDataSourceType.Service)
{
  //Hosted service - can have live attributes - check HasAssociatedFeatureService
}