on the server itself (or through xp_cmdshell on that sql instance) execute
if the server is names like that you will get an output with the ip/hostname of the server the oracle instance is located on.
if tnsping is not found you will need to determine where is the oracle home on that server - this can be done through registry under key HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE
with that you can go to its home, directory network\admin
file tnsnames.ora will contain entries for the oracle server defined on your linked server.
It is also possible that the linked server has the servername on it.