Apex domains cannot have CNAME records.
Question and response
Question
dig tmknet.com.br. NS
Answer
tmknet.com.br. 5 NS ns2.tmknet.com.br.
tmknet.com.br. 5 NS ns1.tmknet.com.br.
Authority
The response has no authority records.
Additional
ns1.tmknet.com.br. 5 A 168.194.191.32
ns2.tmknet.com.br. 5 A 168.194.191.33
ns1.tmknet.com.br. 5 AAAA 2804:339c:30:32:0:0:0:2
ns2.tmknet.com.br. 5 AAAA 2804:339c:30:33:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0