Extract Aether is the "Aerial" Extraction Gathering Skill. Aether is much harder to raise then Extract Vitality for the sole purpose of everything being in the Air. Combined with Flight Time restrictions, most of the time you spend while Extracting Aether will mostly be grounded waiting to fly again.
Since most of your time will be spent on the ground waiting for your Flight Cooldown timer I recommend watching TV, Movie, Browsing the Internet or doing something else in the mean time. It can get quite boring if you just sit there and stare at your screen for a minute every minute.
Anyway, the first place you will want to go for Extract Aether as Asmodian is Altgard. Right above Altgard keep you can find Small Vortex's that will bring your Extract Aether skill to 25. All of the blue dots on my map are the locations of the Small Vortex's that you can harvest.
When your skill reaches 25 you will want to fly higher up into the sky. The higher you go around Altgard, the harder the nodes are to harvest. The "Second level" of nodes is 25. As such, you will want to harvest these until your skill reaches 50. The easiest place to "rest" and recover your Flight Time is definetly at the center island far atop Altgard where Borender sits.
Once your skill hits 50 you'll want to head south to the Impetusium. The easiest way to get there is to fly to Traders Berth from Altgard and head east.
So, I figure that this guide will give you the jist of things but what I can't do is cure your boredom. And lets face it, you're going to be bored. So, here is a set of links with things that I think will entertain you.
My Favorite Band Ever & Favorite Song
Another Amazing Song
Quite Possibly the best Acoustic Cover EVER
The Second Best Acoustic Cover EVER
The Best Cover EVER ... EVER ... I DO MEAN EVER
The Second Best Cover EVER
The Final best Cover EVER (They shoulda just gave the band this song they did so good)
Quite Possibly the best metal song ever
I Write Sins Not Tragedies