Facet of strength - how and where?

Ive already done the mission, but at the time i didnt kow anything about skill capping.
I want to cap gladiators defence for a new build im working on, but i forgot where the misson is :P
Also was wondering how i use the capture signet to actually capture the skill.
how do i know if ive captured it?

It lives in Dragon's Lair
last boss, exclude Glint

Thanks, but where is the dragons lair :O

The Outpost u get to after u acsended

in the crystal desert. Look north.

once the boss has been killed, click the capture signet icon on your skill bar, it will then show you what skills are available to be captured (including greyed out skills that you already have). Just click on the one you are after and then capture....

And that's it.