Get current DNS server on 16.04-server
nslookup can be used to get the DNS server that is being used.
$ nslookup www.google.com Server: 10.0.0.1 <--This is the DNS server address. Address: 10.0.0.1#53 Non-authoritative answer: Name: www.google.com Address: 18.104.22.168
Hope this helps!
For the majority of applications,
should work. Otherwise, you can try,
replacing xxxxxxxx with any server of your choice. You should see what nameserver was used to look it up.
N.B.: Don't be surprised if it is 127.0.0.1 : this is your localhost, which probably means it's your router that is determining your nameserver.