For VST 3 all XLN plug-ins use the standard path set by Steinberg: C:\Program Files\Common Files\VST3
For VST 2:
We're using Addictive Drums 2 in this example, but the same principle applies to all our products.
The most common issue when Addictive Drums 2 doesn't show up in the DAW is that the DAW hasn't found the plug-in file Addictive Drums 2.dll. You may need to change the settings in your DAW so that it is scanning the correct path for the plug-in file.
First of all, run the XLN Online Installer and click on Customize Installation, then head to the Installation paths tab and the VST 2 (64-bit) tab. That page will tell you where the VST 2 64-bit XLN Audio plug-in DLLs are installed.
The next step is to check the preferences in your DAW. The option is usually named Paths, VST paths or Plug-in paths. In those preferences, add the path to the correct plug-in folder and then hit the Rescan button. After that, you should be able to load Addictive Drums 2 like any other virtual instrument.