Documents 6 bankruptcies, and 13 businesses that closed up shop - at the very least suggests he doesn't know what he's doing
While I admit you do have a point but bankruptcies and closing business doesn't necessary mean he doesn't know what he is doing. It could be just the opposite, and show he clearly knows what he is doing.
You have to find out how Trump got into these business and what was happening before hand. Where these business in trouble before he bought them? If so then using the bankruptcy laws to shield himself from debtors while he rearranges the business is a correct and proper business move.
So is knowing when to cut your losses. So closing up show also can show that he knows what he is doing. If the market has changed and there is no hope left, know when to quit is a good thing to know.
Having a business in bankruptcy isn't always a sign that you don't know what you are doing. It could simply mean market forces changed in a way that you didn't see. Or some other crises, that you didn't foresee, have affect your business plans in a manner that you can't adapt to fast enough.
Invoking bankruptcy protection while you change your business around is often used practice. There are a number of highly successful business out there that got a fresh start by going through the bankruptcy process.