Go to ADMIN page and highlight the name of the administrator for which you want to check the last logon time or the last logout time. The time will be displayed in the right side. However, you might has to check each user to find out who logged in or logged out last.
EDIT: Is this query about users logged on to SEPM console or on client computers? The above step is to find the logon details on SEPM console for audit purpose. If you need it for client computers, the logon time details are not captured in SEPM logs.