Hello,
I'm not sure there is an easy way to do this but you should be able to see End Systems in this State by looking in NAC Manager and filtering on the Notification NAC Profile. Go to Tools, End System Operations, Search for End Systems, Advanced. Filter on the NAC Profile "Notification" You can then compare the time that each End System was first placed into this State to the time allocated for Assessment Warning in your configuration. (If the warning time on your config is 10 days and the end system got into that State 5 days ago...you know they have 5 days left) You may also be able to see this on the Statistics tab if you highlight the NAC appliance in NAC Manager, but I am not sure.
Regards,
Scott Keene
NMS/NAC Support