Apex domains cannot have CNAME records.
Question and response
Question
dig dnsx2.pl. NS
Answer
dnsx2.pl. 2 NS ns1.dnsx2.pl.
dnsx2.pl. 2 NS ns2.dnsx2.pl.
dnsx2.pl. 2 NS ns3.dnsx2.pl.
Authority
The response has no authority records.
Additional
ns1.dnsx2.pl. 2 A 96.45.81.1
ns2.dnsx2.pl. 2 A 46.31.237.1
ns3.dnsx2.pl. 2 A 43.247.171.1
ns1.dnsx2.pl. 2 AAAA 2600:180a:4001:0:0:0:0:1
ns2.dnsx2.pl. 2 AAAA 2600:180b:5001:0:0:0:0:1
ns3.dnsx2.pl. 2 AAAA 2600:180c:6001:0:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0