Apex domains cannot have CNAME records.
Question and response
Question
dig com. NS
Answer
com. 5 NS e.gtld-servers.net.
com. 5 NS l.gtld-servers.net.
com. 5 NS k.gtld-servers.net.
com. 5 NS d.gtld-servers.net.
com. 5 NS b.gtld-servers.net.
com. 5 NS h.gtld-servers.net.
com. 5 NS f.gtld-servers.net.
com. 5 NS a.gtld-servers.net.
com. 5 NS i.gtld-servers.net.
com. 5 NS g.gtld-servers.net.
com. 5 NS j.gtld-servers.net.
com. 5 NS c.gtld-servers.net.
com. 5 NS m.gtld-servers.net.
Authority
The response has no authority records.
Additional
a.gtld-servers.net. 157802 A 192.5.6.30
b.gtld-servers.net. 168065 A 192.33.14.30
c.gtld-servers.net. 171458 A 192.26.92.30
d.gtld-servers.net. 97486 A 192.31.80.30
e.gtld-servers.net. 169422 A 192.12.94.30
f.gtld-servers.net. 164501 A 192.35.51.30
g.gtld-servers.net. 164824 A 192.42.93.30
h.gtld-servers.net. 169302 A 192.54.112.30
i.gtld-servers.net. 159738 A 192.43.172.30
j.gtld-servers.net. 164755 A 192.48.79.30
k.gtld-servers.net. 169355 A 192.52.178.30
l.gtld-servers.net. 164911 A 192.41.162.30
m.gtld-servers.net. 169398 A 192.55.83.30
a.gtld-servers.net. 157802 AAAA 2001:503:a83e:0:0:0:2:30
b.gtld-servers.net. 168065 AAAA 2001:503:231d:0:0:0:2:30
c.gtld-servers.net. 171458 AAAA 2001:503:83eb:0:0:0:0:30
d.gtld-servers.net. 97486 AAAA 2001:500:856e:0:0:0:0:30
e.gtld-servers.net. 169422 AAAA 2001:502:1ca1:0:0:0:0:30
f.gtld-servers.net. 164501 AAAA 2001:503:d414:0:0:0:0:30
g.gtld-servers.net. 164824 AAAA 2001:503:eea3:0:0:0:0:30
h.gtld-servers.net. 169302 AAAA 2001:502:8cc:0:0:0:0:30
i.gtld-servers.net. 159738 AAAA 2001:503:39c1:0:0:0:0:30
j.gtld-servers.net. 164755 AAAA 2001:502:7094:0:0:0:0:30
k.gtld-servers.net. 169355 AAAA 2001:503:d2d:0:0:0:0:30
l.gtld-servers.net. 164911 AAAA 2001:500:d937:0:0:0:0:30
m.gtld-servers.net. 169398 AAAA 2001:501:b1f9:0:0:0:0:30
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0