Do you say shana tova gmar chatima tova on yom kippur?

'Shana Tova' means simply 'A Good Year' in Hebrew.'Gmar Chatima Tova' means 'A Good and Significant Finishing' in Hebrew.These are two blessings that the Jews wish to each other at the first 10 days...

This is Hebrew. "Shanah Tovah" == Happy New Year "Gmar hatima tova" is a common greeting/blessing for Yom Kippur that has the meaning of "may you be inscribed in the book of life", i.e., may you...

Only in years where Yom Kippur happens to fall on Shabbat (Saturday). Otherwise, no.

Probably not. You could say, "May you be sealed in the book of life," or "Have an easy fast.". I think it is nicest to say "Have a meaningful fast".

Starting from Sept 12th and until Sept 20th!