Getting back on the horse
It’s been awhile but I started studying with a Jehovah’s Witness again, and I’m going through the “Bible Teach” book with. In our last study, my JW conductor emphatically told me that God’s name, is Jehovah. I asked him what language this name is in; originally that is. (I wanted to tell him it’s a hybrid Latin name but refrained) He said he didn’t know but actually admitted it’s fairly close to the divine name “YHWH”–which is the Hebrew, the tetragrammaton–but that it isn’t his exact name. Of course this an important name according to the Watchtower, they say:
Jehovah wants his name to be exalted. In fact, his primary purpose is to sanctify his name, as is evident in Jesus’ first request in his model prayer: “Let your name be sanctified.” (Matt. 6:9) When making that petition, for what are we praying? 
On a quick side note, the Watchtower seems to take the unequivocal assertion that “sanctifying God’s name”, or making it known, is speaking in the literal sense rather than exuding his renown, his character. When we say things like: the king has a great name, we’re speaking in the colloquial sense. Nevertheless, they say that Jehovah wants us to know and use his name  when citing such verses.
When he told me that the name Jehovah, is close to the original, I said that “if it isn’t his actual name, then it’s a nickname, right?”. At first he was hesitant, and taken aback to my charge–stating again that it’s very close to his name.
I then told him that if it’s not his actual name, then by default it’s a nickname; and that it’s contradictory to claim it’s close to his name while at the same time claiming it is his actual name. (The law of excluded middle came to mind)
I gave him the example of some Chinese folks that I know where I don’t know how to spell or pronounce their names, so them having a transliterated English name is what they’re known by in the English, has been the result. The same goes for the hybrid name Jehovah. We also talked about and agreed that the closest to the Hebrew, is the name Yahweh.
The Great Epiphany
I also questioned him, that if God wanted us to address him by his proper name for all time, then why would he let the pronunciation going into obscurity after the centuries, as he believes. After these expansions of thought, he did come to the realization that his two statements were indeed a contradiction! With the light bulb going off in his head (new light?) he proceeded to state, that, Jehovah is indeed a NICKNAME.
For those that don’t know much about JW’s, this is no small admission, it’s something that can start the snowball effect. It’s pounded into their heads that Jehovah is God’s name, which is one of their supposed earmarks that they’re the “true religion”, and they the preach/share his name to the world. However, if they’re only sharing a nickname of God, then their nickname or title is no better or worse than Christians using names like Elohim, Adonai, El Elyon etc, considering that they condemn us for doing so.