To find this mob in-game, use BACKSPACE to open the World Search window, then enter Rachel Turnbull in the Search field and click "Search". Remember, the field is case-sensitive and must be entered exactly as shown.
To extract a Skill: You need to un-equip the pieces. Place them in the Skill Extraction interface, select the skill you wish (if there is more than one), and pay 500,000 . Once you have Confirmed, the skill will appear in your Skill UI just like an Elite skill, and the equipment will say Item-Set Skill has been extracted.
To equip a skill for use, Press the "Settings" gear in your lower-right HUD, choose Item-Set Skills, then place your new skill in an empty slot on the Wheel. From there you can drag a copy of the Skill icon to your Action Bars. You can only have 5 Item-Set Skills available at a time, and cannot change them during combat or once Siege War has started.