Apex domains cannot have CNAME records.
Question and response
Question
dig pttk.pl. NS
Answer
pttk.pl. 5 NS ns.janus-it.pl.
pttk.pl. 5 NS dns.oeiizk.waw.pl.
pttk.pl. 5 NS ns0.pttk.pl.
Authority
The response has no authority records.
Additional
dns.oeiizk.waw.pl. 5 A 148.81.108.3
dns.oeiizk.waw.pl. 5 A 212.244.131.3
ns0.pttk.pl. 5 A 213.77.35.126
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0