With KEPServer you have the option of creating a tag within the KEPServer itself or by creating the tag in your Client (Ignition) which they call a Dynamic Tag. I think most people do Dynamic Tags, but creating tags in the KEPServer can have some advantages in certain projects.
Your example shows a Dynamic Tag, where the Client (Ignition) is telling KEPServer, please give me the data that resides in memory address 400001 as a Short, from Device1, under Channel 1. But you also need to supply KEPServer two other pieces of information, the Namespace and Address type (not to be confused with the PLC memory address type). In my projects the namespace has always been 2, and the Address type is coming from Ignition is in string format, so your address in Ignition would be -
ns=2:s=Channel1.Device1.400001@ShortPage 19 takes about the namespace and address type - http://www.kepware.com/Support_Center/SupportDocuments/Help/opcuaclient.pdf
If you want to double check the syntax, create a tag in KEPServer and then use Ignition to browse for the tag and add the tag, then check the OPC Item Path for the correct syntax.