Apex domains cannot have CNAME records.
Question and response
Question
dig es. NS
Answer
es. 5 NS g.nic.es.
es. 5 NS h.nic.es.
es. 5 NS a.nic.es.
es. 5 NS c.nic.es.
Authority
The response has no authority records.
Additional
a.nic.es. 155327 A 194.69.254.1
c.nic.es. 162186 A 194.0.34.53
g.nic.es. 172238 A 204.61.217.1
h.nic.es. 162186 A 194.0.33.53
a.nic.es. 155327 AAAA 2001:67c:21cc:2000:0:0:64:41
c.nic.es. 162186 AAAA 2001:678:44:0:0:0:0:53
g.nic.es. 172238 AAAA 2001:500:14:7001:ad:0:0:1
h.nic.es. 162186 AAAA 2001:678:40:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0