First you will want to add traditional insulation between the studs this can be batt insulation spray foam or even rigid foam insulation.
Attic knee wall insulation.
Any penetration between the conditioned interior air and the knee wall space needs to be sealed tight.
I call this tin foil on steroids because that s what it is.
The fourth point is between the roof rafters over the knee wall top plate.
Knee walls that share space with a conditioned room in your home should have a combination of both traditional insulation and foil radiant barrier insulation.
There are two ways to insulate triangular attics behind kneewalls.
How to insulate knee walls.
The main purpose of this material is to seal the fiberglass batts.
Then you can add atticfoil on top of the traditional insulation by stapling it to the wall studs.
The third point is the knee wall and crawlspace floor drywall.
Knee walls have r 13 fiberglass rolls also called batts in them covered with stapled on reflective insulation.
The traditional approach is to insulate the kneewall and the attic floor behind the kneewall.
A better approach is to insulate the roof slope above the attic.
This includes built ins recessed lights vent fans duct work and electrical outlets.
Install a continuous air barrier on the exterior side of the attic knee wall framing with a rigid air barrier or other supporting material to prevent the knee wall cavity insulation from sagging and to create a continuous thermal barrier.