Next to windows, you can always count on there being a stud.
When I read your question, I think you should ask yourself a few questions before you start installing vents. You may already be aware of this, but I thought it was worth mentioning.
Do you have poor indoor air quality today?
Have you changed your heating system, making natural ventilation work poorly?
Have you replaced windows, making the house tighter and therefore having poor natural ventilation?
Is next to the mentioned window the best place for a fresh air vent in your house?
Mockfjärds elementhus seems to be a construction with plank walls, at least until 1973.
Now, I don't think a fresh air vent will jeopardize any kind of safety in your wall construction, but you might want to give this guy a call and ask for advice:
http://www.czbygg.se/menysidor/Elementhusmontor_244
He seems to have worked with mockfjärds elementhus during that time.
Good luck!