Every state has it’s own written exam format, but all the test questions and answers are nearly identical. For example, in Florida the written exam is taken on a computer and each question has a time limit. In New Jersey the written test is taken on paper and there is no time limit. Every state has to conform to federal law which forces all the states to have similar tests.
In most states the general knowledge test is 50 questions and the rest of the endorsements are about 25 questions. You can take as many permit tests as you want in one day. You can always go back to the DMV to get more endorsements. For example, when you first took the written test you only wanted to drive a combination vehicle with air brakes. Ten years later you now want to drive a school bus, so you can go back to the D.M.V and take the school bus endorsement test.
If you want to drive a tractor trailer equipped with air brakes and transporting hazardous material, you must take the general knowledge exam, the combination vehicle test, the air brakes endorsement test, and the hazmat endorsement test. If you want to drive a box truck with hydraulic brakes you are only required to pass the general knowledge exam.
Most perspective commercial drivers take the bare minimum of endorsement tests needed to get begin training and get their commercial license. Usually the bare minimum consists of the general knowledge test and the air brakes endorsement test.