Is there a way to determine the license key that was used to install Professional?
From the design surface in Visual Studio, add a control to a Form and right click it. In the context menu, click "About". This should bring up a dialog with info about your installation, including the key.
I am using VS 2015 & v15.2 of the WPF controls. The context menu does not have an "About" option. We do not use WinForms.
I created a WinForm application to try the solution. It worked.