The Moscow terminal for trains to/from Kiev and several eastern and central European destinations including Belgrade, Zagreb, Bucharest, Budapest, Prague, Vienna, and Venice, Kiev Station is a little under 15 km by road from the Cosmos Hotel.
By taxi
The journey from the station to the Cosmos Hotel by taxi should take about 30 minutes, but can take much longer during rush hour. Taxis will cost $20-30, or you can book a transfer with a driver to meet your train here.
By metro
Take the metro from Kievskaya Metro Station (connected by subway to the mainline station) and travel four stops clockwise on the brown circle line to Prospekt Mira. Change there to the orange line and travel three stops north to VDNKh Station, which is under five minutes on foot from the Cosmos Hotel.