Multiple railways stop at the station Bern Wankdorf. Once you've arrived you have to walk 10min along the Stauffacherstrasse (north of the station) until you reach the Scheibenstrasse 64.

SBB Timetable

Walkway on Google Maps

From Bern main station the Graffitti can be reached by taking the Bernmobil bus line 20 in direction to Bern Wankdorf. Take the stop at Breitfeld and follow the Scheibenstrasse north. Take the turn right after the web transfer. After a few steps you're already there.

Bernmobil timetable line 20

Walkway on Google Maps

It's best to ask your car navigation system;-)