I have a 2000 passat 2.8 v6 wagon, and have owned a 1999 passat 2.8 v6 sedan. I have been told by VW service departments that the AUTO trans units are SEALED so you cannot add fluid! Not sure about...
Have a look under the trans pan. There are two hex bolts. One is 17mm (that's for filling), the other is 8mm (that's for draining). Fill using an oil pump ($5 from SuperCheap) until the oil flows...
I guess that you are puzzled by the lack of a transmission dipstick....there isn't one! See the following site for an illustrated guide to changing/checking the auto-transmission fluid....