Where do I enter info from form 940? I have one employee and use a payroll processor to do payroll.

Yes, you may report your payroll expenses for your business. But first make sure you told TurboTax that you "have employees." You'll find this under your Business Profile on the page "Tell Us About Your Business." 

When you check the box for "I have employees in my business," TurboTax automatically adds Wages under Business Expenses. Enter your payroll taxes under Taxes/Licenses. If you have other employee-related costs, you'll find those listed under Business Expenses as well. Or you can enter them under Other Business Expenses with a custom description. Where you enter your business expenses is not as important as reporting an expense only once.