Find a userA who has GenericAll rights over the userB using Active Directory Recon
Solution 1:
Get-ObjectAcl -SamAccountName joe.blane | ?{$_.ActiveDirectoryRights -eq "GenericAll"}
then
Convert-SidToName <SID>
Get-ObjectAcl -SamAccountName joe.blane | ?{$_.ActiveDirectoryRights -eq "GenericAll"}
then
Convert-SidToName <SID>