Check it first, a lot of the export CRDs had an LSD as standard.
Jack up both rear wheels and spin one, if the opposite wheel spins the same way you have an LSD, if it turns the opposite way you have an open diff.
This is nowhere near definitive. I speak from experience, as my Renegade had a LSD that was shot and acted like an open diff.
If it's open, the carrier is shaped differently. There is only one insertable locker for the LSD carrier, and it's twice the price of the rest.
I swapped in an open diff of the same year (make sure you get one with the proper VSD or ABS sensors, the door jamb 'break date' isn't completely accurate). I drove it open for 6 months and put an Aussie locker in it a couple weeks ago. Love it.
Sorry, just noticed you asked about selectable lockers. If you're going that way, you're looking at $1000 plus ring and pinion setup work. That being the case, Go ARB or forget it. Concerns about broken air lines are easily addressed with careful routing and air line selection. Yes you need to find a place to add an air compressor (or work it off of a 20lb CO2 tank), but it's not like that's the only thing you'll be using your OBA for. If you're serious about a selective locker, you should be serious about airing up/down as well.