Hello there, @LaurieDeCarlo.

The class data that'll be displayed on the Transaction Detail report will depend on how you set up your company preferences. You have the option to assign a class to Accounts, Items, and Names in QuickBooks Desktop (QBDT). With this, let's check your class tracking preferences. This way, you're able to identify why some transactions show empty class fields on the report.

1. Go to the Edit menu.
2. Choose Preferences.
3. Select Accounting from the left menu.
4. Choose the Company Preferences tab.
5. Under the CLASS section, put a checkmark to Use class tracking for transaction.
6. Check the box beside Assign classes to, and then select options (Accounts, Item, or Names) you'll be assigning class into your reports.

I've attached a screenshot below that shows the last four steps.

To learn more about this, you can refer to this article: How to use class tracking in QuickBooks.

Also, here's an article that'll further guide you in filtering and sorting class transactions through reports by class in QBDT: Categorize data by class. It includes topics about unclassified transactions and reports showing subclasses only, to name a few.

Let me know in the comments below if you have other concerns about customizing reports and managing class transactions in QBDT. I'm just around to help. Take care always.