I’ve been asked about a global copyright certificate a couple of time in the past few weeks. Curious, I checked on google and the first things I found were: it’s not a thing.

There is no global governing body or authority to even enforce a global copyright certificate.
Every country has their own laws regarding copyright and intellectual property protection.
Those countries then sign treaties with other countries to say they will enforce copyright protection for their citizens abroad.

But no global copyright certificate.
As always, if you have questions about copyright to protect your book or IP – contact an intellectual property or IP attorney.