The last time I was at SXF, Aeroflot was flying out of there. You can go to the website for Berlin's airports and look up the flight schedules for the cities served. You didn't mention where it is that you are going on the train? If it's using a IC or ICE train, then
your choices are generally limited to the Hauptbahnhof and either the Sudkreuz/ Gesundbrunnen or Spandau/Ostbahnhof extensions. SXF only has regional train service that will take you to the Ostbahnhof and Hauptbahnhof stations. But whatever you do, avoid using the S-Bahn trains out of SXF.