Thank you!
I did know about vComputer, but I had forgotten!
One modification is to use vComputer.ResourceGuid instead of _ResourceGuid.
I am not sure of what the underscored field refers to, or how to know which to use.
The correct query is thus:
SELECT vc.Name, MAX(cr.StartTime) as LastRequest
FROM Evt_NS_Client_Config_Request cr
JOIN vComputer vc ON vc.Guid=cr.ResourceGuid
GROUP BY vc.Name
ORDER BY vc.Name
And to then find out which machines haven't reported for 14 days:
SELECT vc.Name,
MAX(cr.StartTime) as MaxRequestTime,
DATEDIFF(day,(MAX(cr.StartTime)),GETDATE()) as LastSeen
FROM Evt_NS_Client_Config_Request cr
JOIN vComputer vc ON vc.Guid=cr.ResourceGuid
GROUP BY vc.Name
HAVING DATEDIFF(day,(MAX(cr.StartTime)),GETDATE()) >= 14
ORDER BY LastSeen DESC