Answer :
Answer: Clustering
Explanation: In simple words, clustering refers to a form of communication in which a single person transmits the message to the sub groups and this cycle follows on. The individuals to which message is transmitted are not randomly selected.
In the given case, John wants to know the factors for which the potential customer wants to purchase his brand products. However due to higher population on target individual analysis is not feasible.
Thus, John should opt for Cluster by making subgroups for the flow of information.