Is the DotNetNuke Database Layout Schema an Intellectual property of DotNetNuke Corp or someone else?

AFAIK, your DB schema IS your Intellectual Property or IP

Its the way or methodology used to interface with your clients.

There are many CMS that do the same thing in different ways.
But the DNN way would be protected, from you copying their way. You may be able to use bits of it, like the survey module, but how that module fits into the greater framework is what DNN core does, and that will surely be protected?

Its designed for you to hinge your IP onto the end of their system without the overhead of developing your own similar system, which might never be as good, and would probably not get you a return on your investment. So why reinvent the wheel when we can just change the payload?

So I think the answer to your question is 'Yes' although I don't think that if you copy the schema and replace the code that you would have 'invented' something or couldn't be sued (even if your code actually works) This would definitely be a job for the legal department to provide clarity.

You wouldn't be able to clone this system easily and achieve anything, without copying big chunks of their code, so what would your intent/objective be? What do you think you could achieve by copying their schema? Everything is so tightly integrated that I dont know what the point would be?

This is IMHO, and I don't know if that helps you answer your question at all?