Go to Computer/Applications. If you CTRL-click or right-click on "Cubase SX" you can select "Show Package Contents" to have a look inside.
The executable "Cubase SX" program file is stored here: Contents/Mac OS
You'll also find a VST plug-in folder: Contents/VSTPlugins
It contains the factory VST plug-ins that come with Cubase SX. These plug-ins don't work with any other host application.
Don't alter the SX package content in any way! It may result in erratic operation of Cubase SX.