There is no hook specific to that scenario; you may be able to consider if one of these extensions (Auth0 Management API Webhooks or Auth0 Authentication API Webhooks) can serve your needs. The extensions go through the audit logs and trigger webhooks upon finding certain log entries so it may be possible to detect the email verification action from the audit logs and react accordingly.
Have in mind that the above is not synchronous and I’m even unsure how the verification email gets surfaced to the audit logs so it may not be feasible.