Apex domains cannot have CNAME records.
Question and response
Question
dig nic.es. NS
Answer
nic.es. 4 NS g.nic.es.
nic.es. 4 NS ns1.nic.es.
Authority
The response has no authority records.
Additional
g.nic.es. 4 A 204.61.217.1
ns1.nic.es. 4 A 194.69.254.1
g.nic.es. 4 AAAA 2001:500:14:7001:ad:0:0:1
ns1.nic.es. 4 AAAA 2001:67c:21cc:2000:0:0:64:41
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0