You can use the CLI command: show dns cache
You can also examine the Monitoring > Flows report in the UI and for any given flow of interest, you can click on the details 'i' button.
In there, you can examine the AVC/DNS tab. There you can see the first pkt source and dest domains recorded for the flow.
In more recent versions, you can also see the 'Flow Decision' tab which takes you through the entire policy chain applied to that flow.