Answer:
Ethos
Step-by-step explanation:
Ethos is one of the three Aristotle's elements of good communication that is based on credibility. It explains the reason why a listener should believe what you are saying to them.
This can also come as a result of ones position and in the environment where he is communicating or because of his expertise and skills and knowledge in the subject of communication which actually convince the listeners that you are more knowledgeable.
Ken's position as Dexter's trainers makes allows his credibility to Ken.