Puck may have had access to that information from as far back as "The Mirror". But info gathered by Puck was not info that Owen could give to Xanatos, as a function of their agreement.
I'm not sure Xanatos knew until Owen let it slip in Hunter's Moon, Part Three. By which time the info was useless. I guess what you're missing is that moment when David says, "My god, you mean to tell me they've been in the Clock Tower the whole time?! Why didn't I see that?! I'm such a fool!"
Of course, that's not very Xanatosian, is it? He takes the revelation in stride. As if he'd always known. That's his style.
Then again, maybe he had figured it out long ago.
On some level, I'll leave that decision up to each and every one of you.
2. How was Xanatos able to learn about Iago and Desdemona? How did he find Coldstone in the Himalayas?
Xanatos was able to access Coldstone's memory banks, and had a means to track his cybernetic parts.
3. Does Xanatos give up his scheming ways for good after reaching a peace with Goliath's clan?
Xanatos went through a protracted, gradual change over the course of 65 episodes. Hopefully, you all thought it was organic and believable. But I never said he had stopped scheming. (Keep in mind, I had nothing to do with how he was portrated in the last twelve episodes of CHRONICLES.) I don't even believe that his goals have changed that much. But his priorities have definitely shifted, plus he gained a great deal of self-knowledge and a clearer view of what matters most in life. First and foremost, his family. Second, true friends (or at least allies) that you can really count on. He has learned that you have to give if you ever hope to take. (But that doesn't mean he's done taking.) As to his plans, I still think he wants immortality, so that's not over. And I felt he needed to deal with the Illuminati, who are likely to expect things from him that he's not prepared to deliver. Don't expect his methods to change much.
As to the why, well, frankly, the character demanded it. The relationship with Fox manifested itself to the pleasant surprise of everyone involved. We were all even more surprised (David included) to find out that he actually loved her. Every other step along the way was a natural outgrowth of the revelation that he was capable of love. His father influenced him as well. Though he'd be loathe to admit it, David cares what his Petros thinks of him. It wasn't an accident that Petros was invited to his wedding.
4. How does Xanatos control the wings, laser, and tail of his Steel Clan exoframe?
The suit is run via a personalized control system, with those particular features named above being selected from an options scroll, on the screen in the suit's helmet.
5. Where did the name "Xanatos" come from?
Firstly, it's a variant on the Greek god of death (Thanatos). Second, they found it in a phone book.
6. Why does David Xanatos look so much like his voice actor (Jonathan Frakes)?
It's coincidence, believe it or not. Xanatos was fully designed before Jonathan auditioned for the part. After he took the role, he trimmed his beard in the Xanatos style for a time, but Jonathan's appearance had no influence on Xanatos's appearance.
7. What's that blue patch around Fox's eye?
It's a tattoo, a blue fox-head symbol.
8. Does Owen have a love life? If so, do we know his romantic interest?
Yes, he has a love life, but no, we don't know her. She's human, however.
9. What is Owen Burnett's middle name?
10. When Owen dies, won't Puck die too?
If it's a death from unnatural causes (murder, accident), yes. As for natural causes, one should know that Owen won't be dying of old age anytime soon. Every time Owen turns to Puck and back, Owen is "reset" to his exact physical condition at the time of his creation (except for the stone fist) thanks to a fortunate loophole. Owen will survive for as long as Alex does, and he is still alive by 2198.
11. Is Puck Oberon and Titania's biological child?