Showing the Social Security Numbers (SSN) on the paystub isn't an option.
In most places of QuickBooks, you can only see the last four digits of the employee's SSN. You can run the Employee Details report to see the complete number.
Let me show you how to do it.
Click Reports on the left panel.
Type Employee Details in the search box.
From the report, go to the TAX INFO column and check the employee's Social Security Number.