Poznań (Poland) and Sosnowiec (Poland) are 280 km (174 mi) apart in a straight line. The way we suggest is by train, via Częstochowa: ~4h 40m door to door with 1 change. The fastest route, by flight and train via Katowice, takes ~4h. No flight is needed.
Step by step
Train from Poznań to Częstochowa: ~3h 25m, 235 km
Train from Częstochowa to Sosnowiec: ~1h, 57 km
Every route we know
Train, via Częstochowa: ~4h 40m, 1 change
Train, via Wrocław and Katowice: ~4h 35m, 2 changes
Flight + Train, via Katowice: ~4h, 1 change
Train + Bus, via Wrocław, Katowice and Czeladź: about 5h 15m, 3 changes
Train + Bus + Train, via Częstochowa and Katowice: ~5h 20m, 2 changes
Flight + Bus + Train, via Balice and Kraków: ~5h 45m, 2 changes
Times are rough door-to-door times, with time to change and to get through airports included. A "~" marks a rough time worked out from the distance. We don't have timetables, and fares are rough estimates, not quotes: check Google Maps or the operator before you travel.