Without knowing what unit you want to fit exactly it's anyone's guess what comes with it as standard.
However you will need a CAN bus adapter (do not be tempted to just 'wire it to ignition' - otherwise you're asking for trouble), this should be platform specific. Ask the seller if a mk6 platform spec CAN bus adapter is supplied with the unit, if not get one. The seller will no doubt want to make a sale and may tell you that you can just hard wire it