Q: How do I reset an ipad if the original owner is deceased  and the iCloud id is not known?

The executor would need to take the device, a copy of the death certificate and if possible a copy of the purchase receipt to a physical Apple Store and they should be able to assist.

It can not, but take it to Apple and they can. You will need a death certificate and proof that ownership has passed to you.

You will need a certified death certificate and proof of ownership by the original owner as well as proof it was sold or given to you by the deceased. Take that and the device to your local Apple retailer for assistance. If it cannot be reset, then it is useless to you. See below:

It requires the Apple ID and password of the previous owner. If you don't have it and cannot get it, then the device is useless to you. Return it for a refund, if you can, or take it to an Apple store for an exchange provided they will help you.

Find My iPhone Activation Lock

In the future check first before buying second hand: How to check for Activation Lock before buying a used iPhone.