Apex domains cannot have CNAME records.
Question and response
Question
dig jettel.pl. NS
Answer
jettel.pl. 1 NS ns2.tld.pl.
jettel.pl. 1 NS ns1.tld.pl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0