When they come to my door, I take them to both John 20:28 and Acts 20:28. They have abused the latter passage by inserting words in their New world translation, but John 20:28 is intact.
Regarding the passage in John, I ask "was Thomas breaking the first commandment by worshipping someone besides Jehovah?" Concerning the second passage, if it is translated correctly, it clearly says that God bled. Since that cannot refer to the divine nature, it has to refer to a human nature, and only Christ has a human nature which did indeed bleed for us. He must be God.
Also, be careful with some of their go-to passages. They like to take you to Colossians 1 to prove that Jesus was created. The NWT says:
"He is the image of the invisible God, the firstborn of all creation; because by means of him all other things were created in the heavens and on the earth, the things visible and the things invisible, whether they are thrones or lordships or governments or authorities. All other things have been created through him and for him."
By inserting the word "other," they place Christ as the first of God's creation by which He then created all other things. This is a violation of the text. Christ being the firstborn does not mean that he was created first, but as the text later says, He is the one with preeminence. This is a reference to primogeniture, not order of creation.