Apex domains cannot have CNAME records.
Question and response
Question
dig upf.edu. NS
Answer
upf.edu. 4 NS ns6.upf.edu.
upf.edu. 4 NS ns3.upf.edu.
upf.edu. 4 NS ns1.upf.edu.
upf.edu. 4 NS ns2.upf.edu.
Authority
The response has no authority records.
Additional
ns2.upf.edu. 4 A 84.89.128.13
ns3.upf.edu. 4 A 84.89.128.14
ns6.upf.edu. 4 A 84.89.128.17
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0