Tracking Consumption of NBA Requests
Track consumption of NBA requests in your org in the Setup –> Company Settings –> Company Information page. There are two published metrics:
In the Usage-based Entitlements section, you’ll find ‘Maximum Next Best Action Requests available’:

This will show, in the Allowance column, the sum of the 5000 monthly ‘freemium’ org allocation and any allocation purchased via the Einstein Next Best Action Additional Requests SKU. The Amount Used column rolls over monthly. Note that it does not roll over on the first day or last day of the month. The rollover date varies from org to org.
Orgs that have been provisioned with the Einstein Next Best Action -Unlimited Requests permission set license will see the available and consumed licenses in the Permission Set Licenses section:

This license is included in several SKUs, including Service Cloud Einstein and Platform Plus. It also gets provisioned when ISV’s incorporate Platform Plus into their ISV Solution. That can be confusing because there’s no clear linkage in the UI between the licenses and the ISV package you’ve installed. Note that when ISV’s do this, their license restricts the use of NBA to their own application, so it’s not allowable to use these licenses for general purpose NBA.
Requests that are generated by users with the Unlimited Requests SKU do not get counted in the Amount Used column of the Usage-Based Entitlements.