LIST OFFICE 365 GLOBAL ADMINISTRATORS VIA POWERSHELL
You need to be an Office Global Administrator to run these commands.
You need to be running Powershell as Admin and you need to download
Microsoft Online Services Sign-In Assistant for IT Professionals RTW
Firstly download and install this software:
Then fire up Powershell as Admin and run the following commands:
This will install the Office 365 Powershell Module
Connect to Your Office 365 Tenant
Use this command to connect to your Office 365 tenant:
Finally run these two commands and it will display all your Global Administrators
$role = Get-MsolRole -RoleName "Company Administrator"
Get-MsolRoleMember -RoleObjectId $role.ObjectId
Using the Portal to List Global Administrators
You can also login to the Office 365 Portal, Click on Admin > Active Users and then select Global Admins in the Views drop down menu: