You would want to enable Audit Logging on your DC. If you don't have auditing enabled now, you won't be able to gather this information until you enable it. The easiest way to do this would be through Group Policy. Open the Group Policy Management Console and right click and choose "Edit..." on the "Default Domain Controller Policy" that is linked to the Domain Controllers container. Drill down to "Computer>Windows>Security Settings>Local Policies>Audit Policy". You'll want to enable the "Audit Account Logon" and audit either "successful" attempts, "failed" attempts, or both.
You haven't mentioned what OS your DC is running. If it's 2008/ 2008 R2 you have some additional Auditing options.
The above settings will generate events in the Security Event log on your DCs when a users logs on to a domain PC. Even with auditing set, you still need to go through your event logs to gather the information.