Since a recent update in master, the Zoom effect is no longer present in the list of effects, and pre-configured hot keys for it do no longer work.
might it be that you are on llvmpipe?
It also does not appear when using XRender, which it previously did.
Git commit b78848ef3683913824f04d168c7881ffd8052801 by Martin Gräßlin. Committed on 24/08/2016 at 14:24. Pushed by graesslin into branch 'master'. [effects] Add enum value for new TouchPoints effect M +1 -0 effects/effect_builtins.h http://commits.kde.org/kwin/b78848ef3683913824f04d168c7881ffd8052801