from cognite.client.data_classes import TransformationNotification
notifications = [TransformationNotification(transformation_id = 1, destination="my@email.com"), TransformationNotification(transformation_external_id="transformation2", destination="other@email.com"))]
res = client.transformations.notifications.create(notifications)

{
  "items": [
    {
      "id": 123,
      "createdTime": 123,
      "lastUpdatedTime": 123,
      "transformationId": 123,
      "destination": "<string>"
    }
  ]
}