It is likely that the knee wall (or the standing studs, i.e. the roof trusses, in them) are load-bearing. The tongue and groove or whatever covers between the roof trusses helps to make the house stable, for example, when it is very windy, as I understand it. This is normal for that type of roof truss and they are also drawn on the sectional drawing. See here: https://www.byggahus.se/sa-fungerar-en-takstol