I have an Indian friend in Germany who just completed his Masters. He has a German job search visa for another year. He can speak decent german and is looking for a job.

I was wondering if it's legally possible for him to search (& join) an internship / job in Switzerland on the same documents he has?
If not, any idea what is the legality involved?

The only use of the German visa in Switzerland is that your friend can visit to search for a job and for interviews.
Anyone wishing to employ him will have to apply for a Swiss work permit for him with the local authorities here, and he will have to apply at a Swiss consulate / embassy in Germany from his end to get an entry visa for long term residency in Switzerland to take up a job.