Apex domains cannot have CNAME records.
Question and response
Question
dig com.pl. NS
Answer
com.pl. 5 NS f-dns.pl.
com.pl. 5 NS b-dns.pl.
com.pl. 5 NS a-dns.pl.
com.pl. 5 NS d-dns.pl.
com.pl. 5 NS j-dns.pl.
com.pl. 5 NS h-dns.pl.
Authority
The response has no authority records.
Additional
a-dns.pl. 65719 A 192.102.225.53
b-dns.pl. 65719 A 192.195.72.53
d-dns.pl. 113805 A 185.159.197.48
f-dns.pl. 172344 A 194.0.25.29
h-dns.pl. 172606 A 185.159.198.48
j-dns.pl. 172572 A 204.61.217.4
a-dns.pl. 65719 AAAA 2001:7f9:0:0:0:0:0:53
b-dns.pl. 65719 AAAA 2001:7f9:c:0:0:0:0:53
d-dns.pl. 113805 AAAA 2620:10a:80aa:0:0:0:0:48
f-dns.pl. 172344 AAAA 2001:678:20:0:0:0:0:29
h-dns.pl. 172606 AAAA 2620:10a:80ab:0:0:0:0:48
j-dns.pl. 172572 AAAA 2001:500:14:7004:ad:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0