Final answer:
At a Commanding Officer's Non-Judicial Punishment (NJP) aboard a ship, an E-4 can be awarded reduction in rank, forfeiture of pay, extra duty, and restriction.
Step-by-step explanation:
At a Commanding Officer's Non-Judicial Punishment (NJP) aboard a ship, an E-4 can be awarded all of the following punishments:
- Reduction in rank: This is when an E-4 is demoted to a lower rank, such as E-3.
 - Forfeiture of pay: This is when an E-4 has some or all of their pay withheld as a punishment.
 - Extra duty: This is when an E-4 is required to perform additional work or tasks as a disciplinary measure.
 - Restriction: This is when an E-4 is confined to a specific area or place as a form of punishment.
 
Therefore, all of the listed punishments can be awarded to an E-4 aboard a ship at a Commanding Officer's NJP.