Answer:
His research method is naturalistic observation.
Step-by-step explanation:
Naturalistic observation refers to observing the subject in its natural context. This type of research method is generally used to get a genuine idea of the subject's life.
In this case, Jack is using this type of research method because he is observing the subjects in their natural context, not in a lab, for example. He is simply observing their reactions to his friend in the elevator without intervening.