Berlin Hauptbahnhof / Central Station
Take the bus line M41 until you reach the stop "Ziegrastraße".
Travelling times:
Berlin Südkreuz
In case your train arrives from the south it is likely that it'll also pass the smaller train station "Südkreuz". From there you can directly take the urban railways S42 (labelled "Ring") until you reach the stop "Sonnenallee".
Travelling times: