First you will have to check if the events 1202 (Scan started) and 1203 (scan completed) are already enabled on ePO or not. By default they are not enabled, this you can check on Configuration - Server Settings - Event Filtering.
After enabling these events you will have to wait that your workstations/servers get this new information or you can force using an agent wake up call.
Then you can create a query to list only the events 1202 and 1203 based on Events Generated within "x" hours or days.
Attached you have a query that you can import on your ePO server to see the results, this might help you.
hope this helps.
Thanks for your help!