$ uname -a
Darwin starkair.lan 18.7.0 Darwin Kernel Version 18.7.0: Tue Aug 20 16:57:14 PDT 2019; root:xnu-4903.271.2~2/RELEASE_X86_64 x86_64

$ brew list zsh
/usr/local/Cellar/zsh/5.7.1/bin/zsh
...

$ source <(kn completion --zsh)
_arguments:comparguments:319: can only be called from completion function
_arguments:comparguments:319: can only be called from completion function