What kinds of knives are you talking about?
Old traditional pocket knives, slipjoints and lockbacks...etc ?
That can of compressed air will come in handy if you don't have an air compressor, but you'll need to loosen things up.
Skewers, tooth picks, Popsicle sticks that you can shave to shape, an old toothbrush, or a " robot toothbrush" as I like to call them from the hardware store, and most of all some liquid.
Penetrating oil like WD-40, or some warm soapy water, dish soap works great and everybody has it.
A vacuum with a very fine improvised crevice too probably would suck a lot of stuff up / out once loosened ( never thought to try it ) but blowing it out into a shop rag is easiest.
Cotton swabs can catch on things and leave fingers inside, but a piece of blue Scott towel folded over a shaped Popsicle stick works great without leaving fibers stuck to exposed handle scale pins...etc inside.
If we're talking about pinned together traditional pocket knives, obviously with the modern stuff you just use a good driver to take everything apart and don't lose anything.
After it's all dry, oil is important.
I mostly use food grade mineral oil, but a little WD-40 is fine.