Ask them why the Watchtower says Jehovah's Witnesses must 'hate' people who disagree with the teachings of the organization and choose to leave. (see Why Do Jehovah's Witnesses Fear Apostates?) This directly opposes the teachings of Jesus. Jehovah's Witnesses know that Satan's organization opposes God. If Watchtower teachings oppose the teachings of God's son, wouldn't that make them part of Satan's organization?
Read the list of 141 Things Jehovah's Witnesses Can't Do and ask them to show you in the Bible why some of these things are wrong.
If the Watchtower is God's representative and only path through which God saves people, why do they also admit having no divine inspiration? (see What The Watchtower Says About Their Relationship With God.)
Ask them if they are loyal to God and his organization. They will say yes. Then ask them if loyalty to God's organization could be a modern day form of idolatry. They will argue that they worship Jehovah, not the Watchtower Society. If this is true, ask them why everyone needs to belong to the organization to be saved. Why can't people worship God directly without the organization and be saved? Why does everyone need a 'visible representative' of God to be saved? Also ask them what the Bible says about creating an statue, image, or visible representation of God as their object of devotion, loyalty, and obedience. Witnesses know idolatry is forbidden by Jehovah, however when you present them with this unfamiliar concept, they may not immediately see they are condemning themselves with their own beliefs. Keep asking questions to get them thinking. Try to understand their side of the story. Let them talk.
If a Jehovah's Witness challenges the rules of the organization or disagrees with doctrines that are not clearly presented in Bible, can they get disfellowshipped and lose out on everlasting life? If so, has the organization added to God's word?
When will armageddon come and how can we be sure the Watchtower is correct about this doctrine if they've been wrong so many times before.
Why didn't the end of the world come in 1975 like the Watchtower thought it would? Don't they claim to be the only true religion in the world? If they have the truth and God's direction, why was the slave wrong again. Careful with this one. Most Jehovah's Witnesses reject the idea they ever predicted the end of the world.
If God speaks through the Watchtower why did he give them 1975 as the date for armageddon? What good reasons do we have to trust anything else Jehovah's Witnesses say is the truth if they were wrong about 1975? See False Prophet
Can you prove to me that the Watchtower isn't a false prophet? If so, why didn't God 'vindicate' his name and 'visible' organization in 1975 by destroying the world and saving only Jehovah's Witnesses? Watch this video Jehovah's Witnesses-Watchtower Society Exposed Part 6 of 7.
Why is mental illness significantly higher in the Jehovah's Witness religion?
Questions related to child abuse allegations within congregations and why the Watchtower settled out of court. Watch these videos: Jehovah's Witnesses Silentlambs March New York and Jehovah's Witnesses on CNN News and NBC News - Jehovah's Witnesses Settle Molestation Cases
Questions related to Theocratic Warfare and 'hiding the truth' from people who 'don't need to know'.
Questions related to who runs the organization. (Jehovah's Witnesses believe it's the 'faithful and discreet slave' or approximately 10,000 members 'anointed' by God.) There is plenty of factual evidence on the internet that this is not true. In fact the June 15, 2009 Watchtower confirms that the Governing Body represents the slave. Read Does The Faithful and Discreet Slave Class Dispense Truth To God's Organization?
Questions related to Law of Christ and conflicts with Watchtower teachings.
How can they have the truth, if it keeps changing?
If Jehovah's Witnesses are honest, why did you see a video of a Jehovah's Witnesses elder with 30 years experience, lie in court under oath?
Why does the new world translation, (or Jehovah's Witness Bible) have so many errors in it?
Ask them if Jehovah's Witnesses are true Christians. They will say yes. Then ask them why Jehovah's Witnesses have run ahead of the teachings of Jesus? (see How To Recognize Christian Apostates.)