Trying to connect two SQL Server databases
Looks like name resolution is not working. Do you have a DNS server? If not, you may have to make entries in the hosts files on both computers to enable name resolution. The hosts file on Windows is at c:\windows\system32\drivers\etc\hosts.
Try using FQDN. If the server is in a different domain, and a host record is not created in DNS, this would be required to resolve. You could also try creating an alias in SQL Server Configuration Manager.