https://frappeframework.com/docs/user/en/guides/basics/hooks
has error.
As a workaround, you can view the file on github: https://github.com/frappe/frappe_docs/blob/master/frappe_docs/www/docs/user/en/guides/basics/hooks.md
That’s been reported here Docs at frappeframework website return Uncaught Server Exception · Issue #10 · frappe/frappe_docs · GitHub