I googled Looker location and it says you have to go to Lumiose, then you'll get a Holo Cast who tells you to go to "Rouge Plaza". There you'll met with Looker (Spoiler alert) and he'll ask you to be his assistant. But this will only happen when you've become the Champion of Kalos. :D You also need to beat a lot of Team Flare guys/girls/men/woman. ;)
Info link; http://www.serebii.net/xy/looker.shtml
