Do I need a concrete job offer before applying as a skilled worker?

You cannot apply as a skilled worker on the basis of looking for work; you need a firm job offer from a named Norwegian employer. The employer typically confirms the offer first, and you use that confirmation when you submit your application.

The position normally has to be full-time, or at least 80% of full-time, and it must require the skilled qualifications you hold. The pay and working conditions cannot be poorer than what is normal in Norway for that type of work.