Hi Isita,
Cerner's FHIR APIs are patient-centric - unfortunately meaning that there is not a workaround for what you've learned in our documentation. As documented, patient is a mandatory search parameter.
"When integrating your application with a client’s production environment you will work with the client to determine the Practitioner and Location ids (Millennium personnel and location codes, respectively) which they want to make available to third-party applications for enabling scheduling functionality."
In the sandbox environment as mentioned in this thread, we will provide you the ids. And as you work through the development process, Cerner will facilitate continued id discovery in new environments.
Thanks,
Max (Cerner)