Hello dotty and
It is near the top of the engine, right side behind the radiator. It is in a black plastic container that has a screw on cover about 3.5" in diameter. There is a filter element inside. You will have to get the filter from a Dodge or Freightliner dealer and be sure to use only Mobil1 synthetic oil and precisely the correct amount. The computers on these engines has very close tolerances for the oil capacity. If you get it wrong it will set off a fault that only a dealer can clear.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7