`zsh` stores its prompt setups and defintions in `/usr/share/zsh/functions/Prompts/`.
So if you want to take a look what `prompt clint` does behind the curtains, first find the right file:
$ ls /usr/share/zsh/functions/Prompts/*clint*
/usr/share/zsh/functions/Prompts/prompt_clint_setup
And open it in your favorite text editor.