The three airports closest to Cottbus are:

• Berlin Tegel TXL
• Berlin Schönefeld SXF
• Dresden DRS

From Tegel airport to Cottbus:
(trip duration approx. 2 hours, price of the ticket 14,50 Euro)
The easiest way is to take the bus "TXL" at the bus stop (in front of Terminal B, the ticket can be purchased at the automatic machines at the bus stop) to Berlin central station (Hauptbanhof). Then there is a regional train (RE2) directly connecting Berlin to Cottbus.
For more detailed information and planning the trip go to the VBB website
Start location: Flughafen Tegel (Airport) (Berlin), Destination: Cottbus, Hauptbahnhof

From Schönefeld airport to Cottbus:
(trip duration approx. 1 hour and 20 minutes, price of the ticket 14,50 Euro)
The train station is located across the street from the airport.
Take the regional train (RB22) to S Königs Wusterhausen Bhf and then change to the train (RE2) to Cottbus.
For more detailed information and planning the trip go to the VBB website
Start location: S Flughafen Berlin-Schönefeld, Destination: Cottbus, Hauptbahnhof

From Dresden airport to Cottbus:
(trip duration approx. 2 hours, price of the ticket approx 20 Euro)
There is an S-Bahn station on the lower ground floor of the Dresden Airport Terminal. The S-Bahn line S2 connects Dresden Airport with Dresden Neustadt (trip duration about 12 minutes) where there are regional traiins to reach Cottbus.
From Dresden Neustadt there is a direct train (RE18) every second hour, and the trip takes approximatevely 1 hour and 40 minutes, or there is a train (RE15) to Ruhland and then the train (RB49) to Cottbus every othe hour (the total duration is approximately the same as the direct train).
For more details, check the website: Deutsche Bahn website