I use nltest to quickly verify what Active Directory Site a machine is in,
nltest /server:machinename /dsgetsite
The other method would be to determine the subnet of the machine, then see what site the subnet is defined in AD Sites and Services.
But if the subnet is not defined in AD, then the machine will be allocated a random site. If this happens and you what to find out what site the machines in, the nltest command is the easiest way.