Your knee wall is not clearly load bearing. It may or may not be load bearing. It may also not have been there when the house was first built, added later so the attic could be finished, and has since become a load bearing component.
To really figure this out, consult with a real structural engineer, not strangers on the internet. A house may be built with unsupported rafters. It works fine for the snow load you get with an uninsulated roof. The lumber is fresh and undamaged. Someone decides to finish the attic, puts in knee walls. Insulates the new finished space. House ages, rafters degrade, crack, etc. Now there's more snow load on the inulsated roof that is also somewhat weaker. The knee wall becomes structural. But it's still resting on the same floor and that floor wasn't built to support a knee wall and a roof so your ceilings below crack and the floors sag from the load too. It's not catastrophic but it's a common thing that happens with knee walls/rafters in finished attics. Bottom line is it's complicated.
In theory, if you knock out some studs in that knee wall and put in properly sized headers you should be fine. However, now you are no longer spreading the load evenly across as many joists in the floor below and the floor may not like that. Now you have a wavy floor and cracked ceilings downstairs.
Or maybe that knee wall is strictly cosmetic. Your rafters are thick old timbers, your floor joists are super-strong and in perfect shape. We can't tell. You're also adding a good amount of weight: all that trim and drawers (not to mention the stuff you're putting in there) is going to be heavy. A good structural engineer should be able to give you a better idea.
