The Institut for Technology Systems (ITS) of the University of Oslo (http://its.uio.no) is located in the Building of UNIK, Gunnar Randers vei 19, 2027 Kjeller.
By public transport you either take the train to Lillestrøm, and then "whatever" bus going to Kjeller. Closest bus stop is "Forskningsparken (Skedsmo)".
Alternatively take a bus going directly from Oslo to Kjeller. ITS has also an own bus schedules for students coming from Ifi to Kjeller, the schedule is available on http://its.uio.no