NJ and PA have a reciprocity agreement which mean you pay taxes on your wages only in your state of domicile (home-state). since these wages are not taxed by the other state you get no tax credit in your-home state.
income other than wages earned in the non-home state is taxed by both states but then you get a credit in your home-state. the credit can be less than the taxes you paid in your non-home state. you need to review the form on your home-state return to see how the tax is calculated
