Apex domains cannot have CNAME records.
Question and response
Question
dig global. NS
Answer
global. 5 NS a0.nic.global.
global. 5 NS b0.nic.global.
global. 5 NS a2.nic.global.
global. 5 NS c0.nic.global.
Authority
The response has no authority records.
Additional
a0.nic.global. 149873 A 65.22.80.1
a2.nic.global. 149873 A 65.22.83.1
b0.nic.global. 158879 A 65.22.81.1
c0.nic.global. 152210 A 65.22.82.1
a0.nic.global. 149873 AAAA 2a01:8840:4e:0:0:0:0:1
a2.nic.global. 149873 AAAA 2a01:8840:51:0:0:0:0:1
b0.nic.global. 158879 AAAA 2a01:8840:4f:0:0:0:0:1
c0.nic.global. 152210 AAAA 2a01:8840:50:0:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0