As a best practice, acknowledge every donation. You can use a report filter to find unacknowledged transactions and soft credits.
Find Unacknowledged Transactions
In reports, letters, and emails, include the Acknowledgement Status filter and select No to find transactions that need to be acknowledged.
Find Unacknowledged Soft Credits
In reports, include the Acknowledgement Status filter and select No.
In letters and emails:
In the Include section, add the Acknowledgement Status filter and select No.
In the Exclude section, remove the Soft Credit filter.