How do I locate the imei number of my iPad mini (wifi model)

Only cellular models have an IMEI number

the unique number of a cellular device is called IMEI

the unique number of a wifi device is called MAC address (the mac part has nothing to do with mac in the apple world though read more)

IMEI https://en.wikipedia.org/wiki/International_Mobile_Station_Equipment_Identity

MAC adress https://en.wikipedia.org/wiki/MAC_address