By plane: The closest airports are Weeze (DE) and Eindhoven (NL). Somewhat larger and better connected, but further away are Amsterdam and Düsseldorf, both of which can be easily reached by public transport. (There are free shuttles from Weeze, Eindhoven, and Amsterdam to Nijmegen, offered by some airlines.)
By public transport: Nijmegen is well connected to other Dutch cities, as well as to Germany. Check 9292 (and the corresponding app) or ns.nl for prizes and connections. In Dutch trains, busses, and train stations you can usually get free wifi.
If you are coming from Germany, you can also use the Deutsche Bahn app, though it usually doesn’t know about delays and sometimes doesn’t have the current information on the busschedule for the bus SB58 Emmerich-Kleve-Nijmegen.
Nijmegen can also be reached by flixbus.
By car: Erasmusplein 1, Nijmegen – there are a few parking lots on campus, all of which you have to pay for. It is possible to park cars in the area around the accommodation, but note that it can be very hard to find parking spots in Nijmegen.
Protip: Most map apps allow you to download content. This means you can use them offline and without using data abroad. So far, googlemaps only supports directions for cars, but not for bikes, walking and trains, in the offlinemode.