How to go Xi'an North train station from Northwestern polytechnical University?

I’m not sure which campus you mean. There are two campuses of this university. I assume it’s friendship campus. Then you can take the bus line 700 from Xigongda Station to Nan Shaomen Station and walk about 200m to take subway line 2 from Nanshaomen Station to Beikezhan Station. Get out of the station, you can see the North train station.