How to View files shared outside of a domain?

To view files shared outside of a domain

As an administrator, you can use the audit and investigation page to run searches related to Drive log events. There you can view a record of actions to see your organization's user activity in Drive. Drive log events to include content your users create in Google Docs, Sheets, Slides, and other Google Workspace apps, and content that your users upload to Drive, such as PDFs and Microsoft Word files. 

Drive log events are only available for Business Standard and Business Plus; one or more Enterprise editions; Education Fundamentals, Education Standard, Teaching and Learning Upgrade, and Education Plus; G Suite Business; Essentials.

Steps to View files shared outside of a domain

• Go to your Google admin console
• On the left, click Reporting > Audit and investigation > Drive log events.
• Click Add a filter, and then select an attribute as Visibility.

• Then select Shared externally.

• Then, click on Apply
• And, click on the search

Now you will find out who has shared the file externally, However, you cannot see with whom this file was shared.

If you turn off external sharing and a user shares a resource with a group that allows external users, data is marked Shared externally in the log, even if the group doesn’t have any external users. However, external users in the group can’t access the shared resource.

Export search result data

• At the top of the search results table, click Export all.

• Enter a name, and click Export.

The export displays below the search results table under Export action results.

• To view the data, click the name of your export.
  The export opens in Google Sheets.