If you look at the sticker inside the front cover of your service book or under the mat in the luggage compartment it will tell you. The 5th line from the top, the left-hand end is the engine type and the right-hand end is the gearbox type.
For example I have a 2.0TDI-140 common rail diesel engine and a s-tronic gearbox and the codes are CBAB and LQV. At the left-hand end of the line above the engine code will be a figure followed by KW. This is the output of the engine in KiloWatts.
A full explanation of what each line means is given on the inside cover of the service book, on the left-hand side under the dealer stamp.