Can you use Ranged Legerdemain when you can't see what you are working on?
For example from around a corner or say to unlock a door that only has a keyhole/lock on the otherside of a closed door.
Ranged Legerdemain (Su)
An arcane trickster can use Disable Device and Sleight of Hand at a range of 30 feet. Working at a distance increases the normal skill check DC by 5, and an arcane trickster cannot take 10 on this check. Any object to be manipulated must weigh 5 pounds or less. She can only use this ability if she has at least 1 rank in the skill being used.
My take is that you can only do what you could do normally, but at a 30' range.
Ie: your keyhole example is fine, while 'around the corner' (I assume not near the corner) is not.
Ultimately, it would also seem to fall under the targeting rules. You must be able to target it in some fashion. A lock is a visible, targetable object while a lock around a corner that you cannot see is not.