I am German and I have a German passport.
I'll be doing an internship in the US with a J1 visa.
Now I'll have the opportunity to visit the company office in Canada.
Will I need a Visa for this and if yes which one?
You don't need a visa for your visit to Canada : Check this link : https://www.canada.ca/en/immigration-refugees-citizenship/services/visit-canada/entry-requirements-country.html You have : 6 months and the eTA is required if arriving by air.
Here is more information about the eTA if you need one : https://www.canada.ca/en/immigration-refugees-citizenship/services/visit-canada/eta/apply.html