Whenever the Geyser Springs is available on the map
Just like in the first Symphonia game, there is a special event at the geyser. Just go there when you have everyone (including Lloyd) in your party and choose to let the girls go first. Then watch a funny and familiar scene and Emil will receive the Peeping Tom title along with Lloyd's title changing from "Eternal Apprentice" to Peeping Tom. I'm not sure however If the title changes affect Lloyd but note that you cannot change his back to Eternal Apprentice.