Last tested: Jul 15, 2020
The Admin > Datagroups page displays the current datagroup value.
If your Looker instance is self-hosted and you would like to check previous values, you can do so in the logs by running:
grep 'UPDATE' looker.log | grep 'datagroupname' | grep 'trigger_value'
Replace datagroupname with the name of the datagroup you're looking for.
You can also see the trigger value in System Activity > PDT Event Log, but it only has data up to the pruning schedule, so only the past few days of data will be shown.