you need Labview: http://www.ni.com/download-labview/
Than you can debug your Libraray with RadPropertyGrid by enter the Path to Labview exe in the Debug Property Page, Start external programm: "c:\Program Files (x86)\National Instruments\LabVIEW 2015\LabVIEW.exe" . Labview called at first the Contructor RadPropertyGridby loading it in the .Net Container at the front panel. You should set the breakpoint inside the Set accessor of SelectedObject Property. It is called if you run the vi.
Possible there is a Debugging problem with Shadow Copying
When LabVIEW calls a .NET assembly, it enables a .NET feature called Shadow Copying.
To disable this feature in LabVIEW 2011 or later, add the INI flag AppDomainSetup_ShadowCopyFiles=False to the LabVIEW.ini file located in the labview directory.
Inside a standard Windows Forms Application there are no problems. But the standard .NET PropertyGrid can also called from Labview. Possible RadPropertyGrid call special properties of the Application Assembly, which are not supported in Labview?
Your Raddock control has no problems inside a Labview .NET Container. See example: https://decibel.ni.com/content/docs/DOC-46494