On my 92 XJ should my front driveshaft spin freely when the jeep is in park?

 

if you have a vac disconnect on the front axle then yes it will.

 

Im not really sure? My friend has an 88 XJ and his spins free and mine don't. Should mine have the vac disconnect?

 

Well then your friends 88 has a vac disconnect and you don't. it came on certain models.
I personally don't like them because of reliability reasons. Some people that have them claim they get more mpg but I don't believe it.

 

Ok I was wondering because mine has a vibration that I am trying to find.

 

you dont have a vac disco on your 92, its not supposed to spin freely