At Trondheim Værnes airport, passengers connecting between two international flights can usually stay in the transit area without going through immigration. If you connect from an international to a domestic flight, you enter the country here: you go through immigration and collect and re-check your bags.
The airport has 2 terminals or concourses (Domestic and Schengen gates, Non-Schengen gates). All of them are connected after security, so you do not need to clear security again to change.