To be certain, you'll need to consult a repair manual specific to your Grand Cherokee's year and model. A Haynes or Chilton manual would be helpful, or you can find diagrams online if you search for "[Your Year] Grand Cherokee 4.0L Crankshaft Position Sensor Location". Using the year will give you much more accurate results.
Important Safety Note: Working on your vehicle's engine can be dangerous. Always disconnect the negative battery terminal before starting any work, and be aware of hot surfaces and moving parts. If you're not comfortable performing this task yourself, it's best to take your vehicle to a qualified mechanic.