Apex domains cannot have CNAME records.
Question and response
Question
dig tvk-net.pl. NS
Answer
tvk-net.pl. 5 NS ns1.tvk-net.pl.
tvk-net.pl. 5 NS 78.31.127.254.
tvk-net.pl. 5 NS 78.31.127.250.
tvk-net.pl. 5 NS ns2.tvk-net.pl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0