I would show them the following :
1)
Watchtower 1972 April 1 p.197 'They Shall Know that a Prophet Was Among Them'
People today can view the creative works. They have at hand the Bible, but it is little read or understood. So, does Jehovah have a prophet to help them, to warn them of dangers and to declare things to come?
IDENTIFYING THE "PROPHET
These questions can be answered in the affirmative. Who is this prophet? ... This "prophet" was not one man, but was a body of men and women. It was the small group of footstep followers of Jesus Christ, known at that time as International Bible Students. Today they are known as Jehovah's Christian witnesses. ... Of course, it is easy to say that this group acts as a "prophet" of God. It is another thing to prove it. The only way that this can be done is to review the record.
....... So It's offical ! Jehovah has a prophet !
2)
Watchtower 1959 January 15 pp.39-41 Down with the Old-Up with the New!
Whom has God actually used as his prophet?
By the historical facts of the case Christendom is beaten back in defeat. Jehovah's witnesses are deeply grateful today that the plain facts show that God has been pleased to use them. ... It has been because Jehovah thrust out his hand of power and touched their lips and put his words in their mouths...
...... Show them that Jehovah has touched their lips with HIS words
3)
Awake! 1993 March 22 pp.3-4 Why So Many False Alarms?
Jehovah's Witnesses, in their eagerness for Jesus' second coming, have suggested dates that turned out to be incorrect. Because of this, some have called them false prophets. Never in these instances, however, did they presume to originate predictions 'in the name of Jehovah.' Never did they say, 'These are the words of Jehovah
.... Show them how they lie to us
Once they can see the lies of the so called Faithful Slave, and their faith in it is rocked, show them the rest of the story.