Paid rent on son’s MN in-state college apartment. He is dependent. He won't file a return. The rent isn’t deduct. but is the prop. tax portion of rent? On Sched A line 7?

You cannot claim a federal tax deduction for property taxes based on rent you paid. 

To be deductible, the tax must be imposed on you, and you must have paid it during your tax year. As a renter (or parent of a renter), the tax is not imposed on you; it is imposed on the property owner. 

Some states allow a renter to claim a property tax credit, a kind of "pass-through" benefit. This credit is generally available only to the individuals who are occupying the rental property.