Can I improve my knock knees with special shoes or other methods?

Not likely. "knock knees" or genu valgum usually stems from your anatomic built which can only be changed with osteotomies (breaking and realigning bones), reserved for severe symptomatic cases. Pt to strengthen the leg muscles can be helpful but won't change your bone alignment.
Probably not. The only true correction for knock knees is surgery. Once the bones have formed the position is stable and therefore a brace or splint would only be of minimal help.