Apex domains cannot have CNAME records.
Question and response
Question
dig bahnhof.se. NS
Answer
bahnhof.se. 5 NS ns2.bahnhof.net.
bahnhof.se. 5 NS ns.bahnhof.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0