This is the “How Can I See the User/Member/Email addresses in a Dynamic Distribution Group” segment from our larger explanation of what Dynamic Distribution Lists are in Office 365 Hosted Exchange, How to Create and Manage an Office 365 Dynamic Distribution List, and How To Display The Users in Dynamic Distribution Group
Easy PowerShell How to Show The Email Addresses in a Dynamic Distribution List
$UserCredential = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection
Import-PSSession $Session -DisableNameChecking
$MyQuery = Get-DynamicDistributionGroup "< YOUR DDG >"
Get-Recipient -RecipientPreviewFilter $MyQuery.RecipientFilter -OrganizationalUnit $FTE.RecipientContainer