If you are flying to Trenčín, the closest international airport is Bratislava. From the airport take a bus to the city's Central Station before boarding a train out to Trenčín.
The city is also accessible by rail with neighbouring Europe, however, many routes may require at least one change. Once in the city, a taxi to the Expo Center will take no more than ten minutes.
It is also possible to walk depending on where you are. For example, it is a 20 minute walk from the city's main railway station.