I have a 2006 CRD with the RB1 Nav radio and CD Changer but mine did not have Sirius built in and I don't have an Antenna like that on the back of my roof. So it is not a GPS antenna more likely its for sirius. I think the GPS antenna is up near the wiper area.
If you have a changer its in the right rear inside quarter panel of the cargo area. KJ's I have seen with out a changer have a storage nook with a net there.
I looked in to buying the Chrysler tunner for sirius since I had siruis already but the module kit was expensive. I was told wires along with the changer so it may mount close to the changer. If you call sirius they can check to see if your Jeep is set up by your vin or they know key sequences to bring up the radios ESN# If you can get the ESN to display that means that there is a satalite tuner installed and that's what they need to set up the subscription on it.
Edit
I found this page on Liberty radios
http://en.wikibooks.org/wiki/Jeep_Liber ... Head_UnitsThe RBK if that page is correct has: single CD, changer controls, Sirius ready but can not display song title/artist info from the sat, 66 watt power, XM adaptor available
it does not support: sirius artist/song display, MP3 palyback, RDS, UConnect, and obvoiusly not GPS or Nav