Apex domains cannot have CNAME records.
Question and response
Question
dig tt.com. NS
Answer
tt.com. 5 NS ns3.apa.at.
tt.com. 5 NS ns4.apa.net.
Authority
The response has no authority records.
Additional
ns3.apa.at. 5 A 192.174.68.100
ns4.apa.net. 5 A 176.97.158.100
ns4.apa.net. 5 AAAA 2001:67c:10b8:0:0:0:0:100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0