Get Office365 Licenses using PowerShell. Associated blog post can be found here https://blog.darrenjrobinson.com/adding-removing-user-office365-licences-using-powershell-and-the-azure-ad-graph-restapi/

AzureLicencesViaGraphAPI.ps1

# Licenses
$Licenses = Invoke-RestMethod -Method Get -Headers @{
    Authorization   = $authenticationResult.CreateAuthorizationHeader()
    'Content-Type'  = "application/json"
} -Uri ("https://graph.windows.net/{0}/subscribedSkus?api-version=1.6" -f $authenticationResult.TenantId)

# All Licenses avail
$Licenses.value.skuPartNumber

# Query to get the skuId for the skuPartNumber of ExchangeStandard_Student
$LicenceToAdd = $Licenses.value.skuId | Where-Object{$licenses.value.skuPartNumber -eq 'EXCHANGESTANDARD_STUDENT'}