Ask, "Do you have the holy spirit within you?"
If they say "No," since only the "anointed" have that privilege according to our doctrine, ask: "If you don't have the holy spirit within you, why are you preaching to me?"
In the New Testament, Christians are said to have the holy spirit within them, not merely to be "guided by" the spirit. It is an indwelling that Witnesses allow only to their "anointed." But the New Testament does not make such a distinction. In fact, the Bible says that Moses had the holy spirit within him, and Moses was not a member of the 144,000. So how can we say that only this group has the holy spirit within them?