Where do I categorize QB payroll subscription service cost on Sch C?

I assume you are asking how to set it up in the QB program itself. The below image should clarify things. In QB click LIST then CHART OF ACCOUNTS. Right-click on Payroll LIabilities and select EDIT. That takes you to the below screen. For the payroll subscription service select "Other Business Expenses" right below Wages Paid as seen in the pull-down menu.

You can classify those under Dues and Licenses or Subscriptions or classify them individually as QB payroll subscriptions in the Other Miscellaneous category, or as part of payroll expenses.

Actually no.  I'm all set on that, but my payroll service subscription through QB renewed in the fall, and that $744 cost  I want to enter on my schedule C.   Not sure if it would go under taxes and licenses?  or maybe legal & professional fees?

I would list it under Other Expenses and use a description such as "QuickBooks Payroll"