What flag should be displayed from the bow of a boat for a Chief of Staff not entitled to a personal or command pennant?

The correct choice for the flag that should be displayed from the bow of a boat for a Chief of Staff who is not entitled to a personal or command pennant is the commission pennant. The commission pennant is used to signify the presence of a commissioned officer who does not have an individual flag. This is particularly relevant for officers in specific roles, such as a Chief of Staff, where the commission pennant represents their authority and position within the naval structure.

In contrast, the other flags mentioned serve different purposes or are reserved for different ranks or roles. The national flag is generally flown to represent the country and is not specific to an individual officer's status. Personal flags are designed for specific high-ranking officers who are entitled to them, which does not apply in this situation. Guest pennants are typically used for visiting dignitaries and are not appropriate for regular officers. Thus, the commission pennant specifically fills the role when the Chief of Staff does not have a personal or command pennant, making it the correct choice in this context.