Okay, it's reasonably straightforward. Front-wheel drive automatic A4s have a continuously-variable transmission called a Multitronic. These need the oil changing every 40,000 miles.
Four-wheel drive (i.e. Quattro) automatic A4s have a traditional automatic gearbox with a torque converter. These do not need an oil change every 40,000 miles.
The DSG is another type of gearbox altogether; it has a dual-clutch system. As far as I know, though, it's not used in A4s, at least not B7s. I do believe that its name has been changed from DSG to Sport-tronic, but I might be wrong on that
All three types of autobox have a mode that allows the driver to select gears manually, in sequence. This is called tiptronic mode.
If the car you are looking at is an A4 3.0TDi V6 Quattro Automatic, then it has a traditional auto with torque converter; i.e. not a multitronic, and not a DSG/Sport-tronic, and it won't need oil changes at 40,000 miles..