Final answer:
To get information about the Account SKUs purchased by a tenant, you should use the PowerShell cmdlet Get-MsolAccountSku, part of the Azure Active Directory PowerShell module.
Step-by-step explanation:
To get information about the Account SKUs that have been purchased by a tenant in a Microsoft environment, one would use PowerShell cmdlets. Specifically, the Get-MsolAccountSku cmdlet is utilized to retrieve this information. This cmdlet is part of the Azure Active Directory PowerShell module and by running it, you can see the list of SKUs (stock-keeping units) and the number of licenses available and consumed for each SKU in your tenant.
Option (a) Contacting Microsoft Sales and (d) Requesting a tenant audit report would not directly give you SKU information. Option (b) checking the Service Health Dashboard is unrelated, as this dashboard provides statuses on service health, not SKU or licensing information.