Ask them to show you in the "New testament" a scripture /any scripture in the "new Testament" that Christians are to be /should be witnesses of Jehovah .?
Also the WTB&TS published "The kingdom Interlinear Of The Christian Greek Scriptures" some time back .
Ask them to show you in this publication of theirs where the Tetragrammaton { 4 Hebrew letters} or its equivalent 4 Greek letters occur in their word for word translation of the Greek into English that they base their New World Translation of the Bible on.
And if neither of them are their then neither should the name/word "Jehovah" be in the "New testament" or the Christian Greek Scriptures as they like to call it.
It is zero on both counts.