I did receive an answer from the WTO Inquiries department, as follows:

Hello,

Thank you for your recent enquiry.

There is no such document. Perhaps you want to know the biggest
Non-trade barriers. This is a concept which is now under discussion at the negotiations on market access for non agricultural products. There are hundreds if not thousands of these barriers as reported by
governments to the WTO. They are: technical regulations, customs
bureaucracy, anti-dumping, labelling requirements, monopoly practices, excessive requirements for inspections an technical specifications, etc.,etc.,etc.

These are now under discussion and perhaps there'll be some compilation documents in the future.

We hope you find this information helpful.

WTO Enquiries