Dogbone bolts to subframe - 20Nm + a further 1/4 turn
Dogbone to gearbox - 40Nm + a further 1/4 turn
The central bolt that holds the bushes together only needs to be pinched up, otherwise you'll feel too much vibration in the car. Probably only something like 10-15Nm, but there are no figures listed that I can find.
oh and found this on google within 30 seconds of searching "a3 8l dog bone torque settings", first search result