In order to get maintenance mode history for a specific computer you can run the following in an Operations Manager Shell:-
Get-SCOMClassInstance -Name “server.mydomain.com” | Get- SCOMMaintenanceMode -History
Replace server.mydomain.com with the FQDN of the server you want to get the Maintenance mode history for.
This applies to SCOM 2012
It will retuen the GUID of the computer