Kossovo is located about 35 km to the South of Slonim. The station's name is Kossovo-Polesskoe, but it's located in the village of Nekhachevo. Your coordinates are exact. But on the map you've mentioned there is neither Slonim, nor Kossovo. At the top of the map you can see only Niechaczewo (Nekhachevo) and St.Kosow (station Kossovo) close to it. Station is "stancia" in Polish. The city of Kossovo is out of this map, it must be right over the top of it. And you are right, Kossovo was in Grodno gubernia (province) in Tsar Russia. At present time it's in Brest region (or province).