I think your question needs some more explaining. When you installed your e-smith server did you leave the DNS server options blank. Or are you wondering when you leave the DNS servers blank what DNS servers does your e-smith server use.
Here is what I think you are asking. When you leave the DNS servers option blank your e-smith server queries the Root name servers. your e-smith server doesnt just query one or two DNS servers. When you use a local caching DNS server, DNS has a file called root.hints. This is what is used when you want to resolve and internet host names. for instance
If you query
www.ebay.com your local server will query the root name server for the "com" root domain, that server inturn will tell your local dns server what DNS servers hold the record for
www.ebay.com.
If this isnt what you were asking, hopefully someone just got a quick DNS primer.
good luck
Jason