Final answer:
The best nursing action is to 2) notify the health care provider.
Step-by-step explanation:
The best nursing action in this situation where the drainage from a chest tube has suddenly ceased is to notify the health care provider. This is because the cessation of drainage may indicate a blockage or a problem with the chest tube, which requires immediate medical attention. Milking the tubing or assessing the patient for coughing or position changing may not address the underlying issue and could potentially cause harm.