Try these for starters.
The Watchtower departs from Biblical teaching when it comes to many important points/truths such as:
1. The Trinity (they say it was invented by the Catholic Church)
2. Salvation by grace (they believe works are necessary)
3. Jesus crucified on the cross (they say it was a stake)
4. Jesus deity (they believe He was the archangel Michael)
5. The bodily resurrection of Jesus (they believe he was raised a spirit)
6. Eternal judgment (they deny hell)
7. The need to be born again (they believe they cannot be born again).
>> 1. The Trinity (they say it was invented by the Catholic Church) <<
It was.
— a Trinitarian Catholic.