Since the SAP connector is not connecting the database directly, you can not select tables as you would do with a normal database.
Instead you need to use the Scriptbuilder application that is installed when you install the SAP connector. Since the actual and detailed content of each SAP instance can vary, you first need to extract the SAP systems Data dictionary into the scripbuilder.
The scriptbuilder will generate a SQL -statement that you can copy and paste into your Qlikview document.
Hope this helps!