Apex domains cannot have CNAME records.
Question and response
Question
dig wkglobal.com. NS
Answer
wkglobal.com. 5 NS ns-584.awsdns-09.net.
wkglobal.com. 5 NS ns-1303.awsdns-34.org.
wkglobal.com. 5 NS ns-1590.awsdns-06.co.uk.
wkglobal.com. 5 NS ns-258.awsdns-32.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0