Hi @UtauyoNASE
Based on my knowledge, you can use the following command in Skype for Business PowerShell:
(Get-CsUser -Filter {RegistrarPool -eq "PoolFQDN"}).count
For more details about this command, you can refer to:
https://video2.skills-academy.com/en-us/powershell/module/skype/get-csuser?view=skype-ps
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