Apex domains cannot have CNAME records.
Question and response
Question
dig coredns.org. NS
Answer
coredns.org. 5 NS ns.coredns.org.
coredns.org. 5 NS ns1.server.eu.
coredns.org. 5 NS ns2.server.eu.
Authority
The response has no authority records.
Additional
ns.coredns.org. 5 A 31.3.105.133
ns1.server.eu. 5 A 77.95.248.206
ns2.server.eu. 5 A 85.119.243.5
ns.coredns.org. 5 AAAA 2a03:7900:105:31:3:105:133:1
ns1.server.eu. 5 AAAA 2a00:1478:20:f:8:772:0:1
ns2.server.eu. 5 AAAA 2a00:e760:100:f:8:1113:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0