public sealed class AnnotationFeatureClassDescription : FeatureClassDescription 

{
  // Must be called within QueuedTask.Run
  void CreateAnnotationFeatureClassUsingExistingAnnotationFeatureClassInDataset(
    Geodatabase geodatabase)
  {
    // Create a Cities annotation feature class inside Places feature dataset using existing annotation feature class 

    // Feature dataset name
    string featureDatasetName = "Places";

    // Annotation feature class name
    string annotationFeatureClassName = "CitiesAnnotation";

    // Create a SchemaBuilder object
    SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

    // Open existing annotation feature class name
    using (AnnotationFeatureClass existingAnnotationFeatureClass = geodatabase.OpenDataset<AnnotationFeatureClass>("ExistingAnnotationFeatureClass"))
    {
      // Create Feature dataset description
      FeatureDatasetDescription featureDatasetDescription = new FeatureDatasetDescription(featureDatasetName, existingAnnotationFeatureClass.GetDefinition().GetSpatialReference());

      // Add the creation of the Places dataset to DDL task
      FeatureDatasetToken featureDatasetToken = schemaBuilder.Create(featureDatasetDescription);

      // Create an annotation feature class description using existing annotation feature class
      AnnotationFeatureClassDescription annotationFeatureClassDescription = new AnnotationFeatureClassDescription(annotationFeatureClassName,
          existingAnnotationFeatureClass.GetDefinition())
      {
        IsAutoCreate = true,
        IsSymbolIDRequired = false,
        IsUpdatedOnShapeChange = true
      };

      // Add the creation of the Cities annotation feature class inside Places feature dataset
      schemaBuilder.Create(new FeatureDatasetDescription(featureDatasetToken),
        annotationFeatureClassDescription);

      // Execute the DDL
      bool success = schemaBuilder.Build();

      // Inspect error messages
      if (!success)
      {
        IReadOnlyList<string> errorMessages = schemaBuilder.ErrorMessages;
        //etc.
      }
    }
  }
}