Apex domains cannot have CNAME records.
Question and response
Question
dig six-group.com. NS
Answer
six-group.com. 5 NS a5-66.akam.net.
six-group.com. 5 NS ns2.six-group.com.
six-group.com. 5 NS a18-67.akam.net.
six-group.com. 5 NS a1-232.akam.net.
six-group.com. 5 NS ns1.six-group.com.
six-group.com. 5 NS a20-65.akam.net.
six-group.com. 5 NS a24-67.akam.net.
Authority
The response has no authority records.
Additional
ns1.six-group.com. 5 A 153.46.97.67
ns2.six-group.com. 5 A 153.46.105.67
a18-67.akam.net. 5 A 95.101.36.67
a18-67.akam.net. 5 AAAA 2600:1480:4800:0:0:0:0:43
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0