AuldSoul has good ones here
Step 5 : Ask them to review the list and verify that any organization that does not measure up cannot be Jehovah's organization. They will verify that an organization would meet these requirements if it is Jehovah's organization. Rephrase the question again; If Jehovah's Witnesses do not meet these requirements, are Jehovah's Witnesses Jehovah's organization? They will probably not answer you. They will be thinking you are an apostate, at this point (if not before), for even asking.
Step 6 : Tell them you have three teachings you want to have Scriptural support for, ni order to determine that Jehovah's Witnesses ARE Jehovah's organization. (1) Ask them to demonstrate Biblically that a person is required to preach BEFORE Christian baptism. (2) Ask them to demonstrate Biblically that the men gathered at Acts 15 were chosen to represent all Christians (a conjectured teaching that they use to lend authority to the Governing Body). (3) Ask them to demonstrate Biblically that elders are authorized to hold secret trials to judge guilt, innocence, or repentance in place of the congregation.
After asking "If Jehovah's Witnesses do not meet these requirements, are Jehovah's Witnesses Jehovah's organization?" it could be pushed harder by asking "An organization that keeps separate from the world would have to stay out of religious and political organizations, right? If an organization joined the United Nations, it would not be Jehovah's organization, right?"
I, personally, will go with
The organization is not infallible and sometimes our current understanding of the scriptures has to be adjusted, right?
The same organization that adjusted it's understanding of Matthew 24:3, 32 (this generation) also wrote the NWT, right?
Could their NWT need current adjustments anywhere else in that chapter?