Is this game finished yet? Is it available on GOG or anywhere? Also what's the subtitle?

Can you please clarify which game you're asking about?

Officially, there is no King's Quest IX. However people sometimes refer to the King's Quest episodic game that The Odd Gentlemen released last year as this, but that is not the official title. All five chapters have been released on Steam, PS3, PS4, XB360, and XBONE, with the bonus epilogue still on the way for those who purchased the complete collection from the start. Each episode has a different subtitle: "A Knight to Remember", "Rubble Without a Cause", "Once Upon a Climb", "Snow Place Like Home", and "The Good Knight". No plans for a GOG release have been announced (but it's on the wishlist).

Unofficially, King's Quest IX was the originally intended title for the fan-made KQ game known as <i>The Silver Lining</i>. Four of the five planned chapters have been released, and the fifth is supposedly due out soon.

I was referring to the Odd Gentlemen game. I thought someone here said that was the official KQ9. Apparently the Odd Gentlemen got the rights to use the characters AND the "King's Quest" name, while Phoenix Online Studios somehow only got the rights to the characters and the locations, but not the actual name "King's Quest."

When you say "Those who purchased the complete collection from the start," do you mean people who purchased each episode the day it came out? Or do you mean people who bought the entire thing at once rather than just each episode individually?

The epilogue is a bonus incentive for those who bought "The Complete Collection". Those who only bought each episode at a time do not get it.