Where is the wheel speed sensor located on a 2004 jeep liberty i heard it may be differential?

On a 2004 Jeep Liberty, the wheel speed sensors are not located in the differential. They're located within the wheel hubs, near the ABS tone ring on each wheel. You'll find one sensor per wheel. To access them, you'll need to remove the wheel and brake caliper. They're usually a fairly straightforward component to locate once the wheel is off.