^the fact is, the best way to solve problems is to be well versed in the underlying theory. As many of us successful exam takers have stated in this forum, for years now, there are really just a few basic theories that underlie most of the Environmental Engineerning field. The biggies are the overall mass balance approach, ideal gas law, growth and decay phenomena, and chemistry principles.
If you understand the underlying principles, you can solve most problems the PE exam will throw at you. The other aspect is to know your references, and to be able to quickly find specific equations. No professor is going to be able to help you with that - only you can do that.
Many of us (myself included) passed the exam without taking a review course, so I have no idea whether or not it would be helpful to have someone explaining the basic principles as a means of studying for the exam. The way I see it, the best thing a review course could do is to establish a study schedule and force you to stick to it, since YOU have to do all the work of learning, not the professor. (and again, you don't need a review course to do that, but for some people I suppose that might be helpful).
Also, when you refer to "code", what do you mean? In the Enviro exam, at least, there really isn't any "code" that overrules anything. There are questions related to federal regulations, of course, and you certainly need to know your way around the U.S. system of environmental regulations, and have access to references that can answer some of the more important requirements. But most questions are engineering, enviro science, and mathematical in nature. I honestly can't think of any "code" that was needed in the exam.