Apex domains cannot have CNAME records.
Question and response
Question
dig watson.ibm.com. NS
Answer
watson.ibm.com. 5 NS dns3.p05.nsone.net.
watson.ibm.com. 5 NS dns2.p05.nsone.net.
watson.ibm.com. 5 NS dns1.p05.nsone.net.
watson.ibm.com. 5 NS dns4.p05.nsone.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0