Apex domains cannot have CNAME records.
Question and response
Question
dig debnet.pl. NS
Answer
debnet.pl. 5 NS dns1.debnet.pl.
debnet.pl. 5 NS dns2.debnet.pl.
Authority
The response has no authority records.
Additional
dns1.debnet.pl. 5 A 91.235.124.30
dns2.debnet.pl. 5 A 91.235.124.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0