Client Management Suite

Any query or report which can show the last OS installation date?

Check the thread

https://www-secure.symantec.com/connect/forums/computers-last-os-installed-date

https://www-secure.symantec.com/connect/forums/operating-system-installation-date

Edit

Query

SELECT vc.Guid as '_ItemGuid',
vc.Name,
oos.[Name],
oos.[Install Date]
FROM vComputer vc
JOIN Inv_OS_Operating_System oos ON oos._ResourceGuid=vc.Guid

Try these query

SELECT sci.Name, inst.InstallDate
FROM vRM_Software_Component_Item sci
JOIN Inv_InstalledSoftware inst
   ON inst._SoftwareComponentGuid = sci.Guidb
WHERE LOWER(sci.Name) LIKE '%Operating System%'

Other

SELECT
vc.Name,
vc.[OS Name],
arp.DisplayName,
arp.DisplayVersion,
arp.InstallDate
FROM
vComputer vC JOIN
Inv_AddRemoveProgram ARP ON vC.Guid = ARP._ResourceGuid
Where
DisplayName like 'Operating System'
ORDER BY vc.Name ASC