On whether it's important for Christians to use the name Jehovah:
Can you show me one verse where Jesus actually utters the name "Jehovah" in a prayer?
There is not a single verse in the New World Translation where Jesus pronounces the name "Jehovah" in a prayer. He refers to a "name" in a couple of places (Matthew chapter 6 and John chapter 17, but he does not pronounce Yahweh or Jehovah there. "Name," of course, means reputation or character in these verses. If it had meant to pronounce the name then Jesus would have done so.
Can you show me one place in the Greek New Testament in the Kingdom Interlinear where the name Jehovah appears?
There are none.
Are there any New Testament Greek manuscripts that contain either Jehovah or Yahweh?
There are none.
Say, for the sake of argument, we accept the theory that the name Jehovah was removed from the Greek New Testament (even though there' s no NT manuscript to show it was there originally): How often does Jesus use the name Jehovah when in his everyday speech -- when he's not quoting the Old Testament?
Hardly any. So far, I've only found 3 possible places in the New World Translation where Jesus is said to pronounce the name Jehovah apart from Old Testament quotations. Jesus used "Father," "God," and "Lord" to describe his heavenly Father in his everyday speech -- even in the New World Translation.
The New World Translation "restores" the name Jehovah to the New Testament (again, with no NT Greek manuscript evidence) a total of 237 times. So, is this the name that is emphasized in the New Testament? How many times does the New Testament use the name "Jesus"?
The Comprehensive Concordance of the NWT has the name Jesus over 900 times in the New Testament. That's nearly a 4 to 1 ratio of emphasizing the name Jesus over the name Jehovah in the New Testament. Even if we exempt the Gospels for this comparison, the name Jesus occurs way over a 3 to 1 ratio over the name Jehovah in the rest of the New Testament in the NWT. And, in actual fact, since no Greek New Testament manuscript contains the name Jehovah in it, then the name that is emphasized in the NT is clearly that of Jesus.