Apex domains cannot have CNAME records.
Question and response
Question
dig tracking.socketlabs.com. NS
Answer
tracking.socketlabs.com. 5 NS ns-749.awsdns-29.net.
tracking.socketlabs.com. 5 NS ns-1898.awsdns-45.co.uk.
tracking.socketlabs.com. 5 NS ns-12.awsdns-01.com.
tracking.socketlabs.com. 5 NS ns-1449.awsdns-53.org.
Authority
The response has no authority records.
Additional
ns-12.awsdns-01.com. 2 A 205.251.192.12
ns-749.awsdns-29.net. 2 A 205.251.194.237
ns-1449.awsdns-53.org. 2 A 205.251.197.169
ns-1898.awsdns-45.co.uk. 2 A 205.251.199.106
ns-12.awsdns-01.com. 2 AAAA 2600:9000:5300:c00:0:0:0:1
ns-749.awsdns-29.net. 2 AAAA 2600:9000:5302:ed00:0:0:0:1
ns-1449.awsdns-53.org. 2 AAAA 2600:9000:5305:a900:0:0:0:1
ns-1898.awsdns-45.co.uk. 2 AAAA 2600:9000:5307:6a00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0