Ljubljana Airport is directly reachable from: Amsterdam, Brussels, Frankfurt, Munich, Paris, Vienna, Zurich. Timetable with all connections can be found at timetable.
From the Airport the transport possibilities are outlined in the transport page. Take care when taking a taxi: the ones just outside the airport building are relatively expensive (about 50 EUR for a trip downtown). Cheaper service can be ordered by phone or e-mail/web form; e.g.: Taxi Metro and Intertours. They should bring you to the city centre for less than 30 EUR.
The Jozef Stefan Institute is about 2 km from Ljubljana city centre, so access on foot is possible and the walk can be quite pleasant in nice weather (directions). Otherwise. taxis are affordable - the ride should cost you about 5 EUR. You might also consider public transport; Bus #1 stops right in front of JSI. But make sure you have the prepaid Urbana card with you - payment on the bus is not possible!
