Which bus do I take from S-Bahn station Dachau to
The station is located almost in Freisingerstrasse. So no bus, just walk. See here on Google Maps:
keep in Mind that the Dachau Stadt Station Trekki refers to is only serviced by S-Bahn Line A, which only runs once an hour or so (see MVV plan here: [original link]).
You will need to change at Dachau station.
(Timetable for S-Bahn A: [original link] )
Depending on how far out on Freisinger Strasse you will need to go, you can take the 722 Bus (towards Dachau Stadt station) or the 725.
(see here [original link])
To be honest, if I were you, I'd take a taxi ;-)