Since Lansweeper 5.3, the scanning service remembers the last successful credential per asset in order to avoid delay by using wrong credentials. However, this information is not stored in the database and can't be pulled out with reports.
The only thing what you can do on Windows computers is deploying a package under scanning credentials and afterwards having a look at the deployment logs. The log will indicate which credential was used on the machine.
In general, Lansweeper tries credentials as you mapped them to the IP range or IP addresses of assets under
Configuration\Scanning credentials, section
Credential Mapping, from the top to the bottom. Global credentials will always be the last try.