Apex domains cannot have CNAME records.
Question and response
Question
dig ns0.com. NS
Answer
ns0.com. 4 NS ns1.pair.com.
ns0.com. 4 NS pdns0.pit.pair.net.
ns0.com. 4 NS ns0.ns0.com.
ns0.com. 4 NS ns00.ns0.com.
ns0.com. 4 NS pdns0.den.pair.net.
Authority
The response has no authority records.
Additional
ns0.ns0.com. 4 A 216.92.55.21
ns00.ns0.com. 4 A 216.92.60.60
pdns0.den.pair.net. 4 A 216.146.198.35
pdns0.pit.pair.net. 4 A 216.92.19.39
ns0.ns0.com. 4 AAAA 2607:f440:0:0:0:0:d85c:3715
ns00.ns0.com. 4 AAAA 2607:f440:0:0:0:0:d85c:3c3c
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0