If you travel via Schiphol Airport, you can take a direct train to Groningen every hour at 3 minutes past the hour. Every hour at 33 minutes past there is a train that requires you to change trains once (just crossing the platform in Zwolle). Klick here for schedules. The train takes 2 hours and 10 minutes. Tickets can be bought at machines at the airport.
The conference will be held at the Factulty of Philosophy, Oude Boteringestraat 52, in the city center. The faculty building can be entered through an entrance at the side, which is located in a small alley to the right of the faculty building.