Apex domains cannot have CNAME records.
Question and response
Question
dig oktaweb.pl. NS
Answer
oktaweb.pl. 5 NS ns2.oktaweb.pl.
oktaweb.pl. 5 NS ns1.oktaweb.pl.
oktaweb.pl. 5 NS ns3.oktaweb.pl.
Authority
The response has no authority records.
Additional
ns1.oktaweb.pl. 5 A 77.65.163.16
ns2.oktaweb.pl. 5 A 79.98.145.34
ns3.oktaweb.pl. 5 A 193.70.13.218
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0