I live in PA and my spouse is a student in OH. If I file jointly for Federal and separately for state?
If so, can't find any rule which allows me to do that.
Any detailed reply would be appreciated. Thanks.

I suggest the Federal joint and separate for the states. I would try it both ways where you do a joint return for all of PA's income for you both and then her state income for OH. Try it both ways and choose which situation pays the least taxes.