I am using Adobe Illustrator Draw, but it is a very limited app. Is there a professional illustration tool on iPad Pro?
It’s debatable whether any iPad apps are truly “professional” yet, but there are many that come close.
The most Illustrator like app that I have found is Graphic - illustration and design by Indeeo, Inc. https://itunes.apple.com/gb/app/graphic-illustration-and-design/id363317633?mt=8 (UK App Store link, hopefully it will redirect you.)
It’s not cheap for an app, but it’s very good.
There are others such and Concepts and ProCreate that are worth looking at, but I would consider all of these as complementary to using Photoshop, Illustrator etc rather than replacements for them. So far.