The UmbHost UmbSmall, UmbOne, UmbTen, UmbTwenty and UmbLimited nameservers will be provided in your "New Account Information" email, alternatively, you can view them in your account here:
https://umbhost.net/clients/manage-dns-zones
The WPOne or UmbOne (Linux) nameservers are:
ns1.stackdns.com
ns2.stackdns.com
ns3.stackdns.com
ns4.stackdns.com