The block heater on a 2006 Jeep Liberty CRD is located on the
engine block, near the thermostat housing. It's often a cord that extends down from the engine near the lower radiator hose area. You might need a flashlight to see it clearly.
Because its position can vary slightly depending on the specific engine configuration, it's best to refer to your owner's manual for the precise location and instructions on how to use it.