You mean the Graph API query, or? For any of the SDK cmdlets, you can add the -Verbose/-Debug parameters to get the URL called on the backend. So for the above (with some formatting issues fixed) we have:
Get-MgUser -Filter "userType eq 'Guest' and externalUserState eq 'PendingAcceptance'" -All -Property CreatedDateTime
which translates to:
GET https://graph.microsoft.com/beta/users?$filter=userType eq %27Guest%27 and externalUserState eq %27PendingAcceptance%27&$select=CreatedDateTime