How do you remove oil filler cap jeep liberty 3.6?

FilLer cap or filTer cap? And what year?

FilLer cap just turn it counter clockwise. If cap is extra tight or stuck use a large adjustable wrench ( crescent wrench) or slip joint off set pliers ( channel locks) that will grip as much of handle on cap as possible, short jaws may break it. Hold wrench close to jaws and gently turn counter clockwise. It's a good idea to wrap a few layers of cloth or several layers of tape around tab as a cushion.

If cap has knurled finger grip rim instead of tab handle you'll need a pipe wrench or large channel locks, padding again and gentle force, don't squueeze pliers too tight. Sometimes all you need is a rag to pad hand to get tight cover off.

FilTer is easiest with a 24mm socket and extension. On top center front of "engine cover" is an access hole. Most years the access cover is removed by a short counter clockwise turn. I have heard but do know for sure, that some models have a flip up access cover. With access hole open you can reach cap with socket.

I am not personally familiar with 3.6 in Jeep, only in Chrysler so details such as access cover type and filler cap style may be different. But I wouldn't think so.

If you don't have an extension or socket you can remove entire engine cover, and use box end wrench. Engine cover snaps off. Below is a link to you tube, showing how. Also link to online owner's manual, which may help.

Bonus info:

You should get a good quality ratchet handle and medium quality socket set for routine maintenance anyway. Replace sockets as they wear out with quality ones. If you do much driving in the boonies or mare than routine maintenence get quality sickets to begin with. But it's not so cool to ruin a socket getting oil drain plug out and no way to tighten it back, so get best sockets you can afford.