If your question is more about whether Prism Pro licensing is needed for Flow to work or can it work on Prism (AOS) licensing, then in this case you will need an add-On Flow license (separate from Prism (AOS) and Prism Pro license). If you have not installed a Flow license yet, then you can try this feature for a period of 60 days. After this period expires, you will be required to install flow license to continue using the feature. Kindly refer to Add-Ons Licensing guide on Portal for more details about Flow licensing. 

Also, in case if your question was more about whether Prism Central is needed for Flow to work or can you use Flow only with Prism Element cluster, then the answer is no. You will need to have Prism Central in your cluster in order to use Flow. For more details, please refer to the Flow Requirements documentation available on Nutanix Support Portal. 

Kindly let me know if you have any more questions on this one!