Apex domains cannot have CNAME records.
Question and response
Question
dig cdk.com. NS
Answer
cdk.com. 5 NS ns.las.us.cdk.com.
cdk.com. 5 NS ns.ord.us.cdk.com.
Authority
The response has no authority records.
Additional
ns.las.us.cdk.com. 5 A 207.186.148.53
ns.ord.us.cdk.com. 5 A 207.186.164.53
ns.las.us.cdk.com. 5 AAAA 2620:1f8:f012:ffff:207:186:148:53
ns.ord.us.cdk.com. 5 AAAA 2620:1f8:f011:ffff:207:186:164:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0