KMS

Key Management Service (KMS) clients use DNS to locate a KMS server.  The DNS entry is a SRV type  with a name of _VLMCS

slmgr /dlv on the client to display the license information and which server has been selected for KMS.

this command queries the DNS for the KMS server addresses.
nslookup -type=SRV _vlmcs._tcp.<forward lookup zone>

Use cscript slmgr.vbs to get screen text output.  The default just pops up text windows which can be useless if there is a lot of text.

More information here https://technet.microsoft.com/en-us/library/ff793434.aspx

Some Microsoft products which are volume licensed use KMS servers to activate. Office 2016 is an example run the following to check the activation status.

change directory to C:\Program Files (x86)\Microsoft Office\Office16
run

cscript ospp.vbs /dstatus