I use the King James Version when talking to people of the Jehovah's Witness faith, because I don't trust the New World Translation and most of them somewhat trust the King James Version. 

    First read Rev. 1:8 to them which says in the KJV "I am Alpha and Omega, the beginning and the ending, saith the Lord, which is, and which was, and which is to come, the Almighty."

   Ask them who is the Alpha and Omega in this verse, they will have to say Jehovah because the version Jehovah's Witnesses use says Jehovah.

     Next read Revelation 21:6-7 which says "And he said unto me, It is done. I am Alpha and Omega, the beginning and the end. I will give unto him that is athirst of the fountain of the water of life freely.  He that overcometh shall inherit all things; and I will be his God, and he shall be my son." 

    Ask  who is the Beginning and the End,  in this verse. They should respond Jehovah again because they have already said that the Alpha and Omega is Jehovah.

    Then read Rev. 22:12-13 "And, behold, I come quickly; and my reward is with me, to give every man according as his work shall be. I am Alpha and Omega, the beginning and the end, the first and the last." Say, If the Alpha and Omega is Jehovah, the Beginning and the End is Jehovah, then the First and the Last should be Jehovah as well, do you agree?  When they say yes continue reading the passage down to verse 16, which identifies the speaker as Jesus. At this point they will start getting antsy and try to convince you the speaker has changed in the passage. Then just say ok, and ask them again if the First and the Last is Jehovah.  When they say yes tell them just one more passage. 

    Read Rev. 1:17-18 "And when I saw him, I fell at his feet as dead. And he laid his right hand upon me, saying unto me, Fear not; I am the first and the last:  I am he that liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death. "

The speaker here says he was dead, when did Jehovah die?

    If they try to fight you on this point remind them that they said that Jehovah was the Alpha and Omega the Beginning and the End, the First and the last.  If they were right when they said that then Jehovah must have died at some point, and you would like to know when, If they were wrong then Jesus is the Alpha and Omega, the Beginning and the End the First and the Last,  and Almighty (Rev. 1:8)

At this point they will probably claim to remember an appointment and hurriedly excuse themselves.
    When they do hand  both of them pieces of paper with those verses written down on it along with your phone number. And invite them to call you back if they have any more thoughts on the subject.

Handing one to each person enables them to come back secretly if one is so inclined, if you had the paper to just one, they may not let the other have access to it.