Structures vs Tables and Using the SQL Trace ST05

I guess you have looked at a standard SAP transaction and fit F1 help, followed by F9 technical information on a field?

You were hoping to find where the data was stored for a given transaction?

SAP often selects data from the database (Tables) and then formats it before presenting it on the screen. Often it creates structures with specific fields (which may span many tables) to display on the screen.

To find where the data is actually stored you need to dig deeper than just the structure:

Using the SQL Trace 

Open a new session with transaction ST05, select SQL Trace, click on the Trace On button, and go back to your transaction (while leaving the session with ST05 open). Submit your transaction, and go back to the ST05 session. Click on the Trace Off button, then select the List Trace button. Continue with standard selections, and a BASIC TRACE LIST will appear. search through the tables displayed under ObjectName.

SAP Library Link: SQL Trace