The requirement of residence means that you must have an address in Denmark and that this address may be considered to be your actual residence. The address must also be considered as your current and usual place of residence.
The assessment of whether the residence requirement is met is based in first place on the public registered address. However, it is not a condition for fulfilling the residence requirement that you had a public registered address, i.e registered as a member of the CPR (residence register), the day before the start of your education.
If you have not been registered in the public address register (CPR) 1 day before and again 14 days after (when you claims to have been domiciled in Denmark), it is up to you to prove that you have been resident in Denmark.
It must be a real residence. A mailbox address or poste restante is not sufficient.
A landlord's statement that you have rented a property from a given date may be sufficient proof of a place of residence.
But the A-kasse must make a concrete assessment in each case.