Translation:I am singing with my employer at my workplace.
Your boss is not always the employer, so you would use 'sjef' instead if you meant 'boss'.
It's a possible translation in some contexts, because 'boss' and 'employer' are often synonymous, but it's not the preferred translation.
Does Norwegian have a word order rule like the German one about time, manner, place?
Yes, I think so, but I don't think it is very strict. At least I would know when a sentence feels awkward, but it could be altered for emphasis. Both the sentences "Hun løper ofte fort" and "Hun løper fort ofte" would both sound natural, with a slight preference to the first sentence, but when you add a place, I would definitely use the form "Hun løper ofte fort ute". "Hun løper ute ofte fort" would, for example, be very strange. I guess the short answer would be that Norwegian follows time, manner, place.