It's just a written test. You go to your DMV and take the test, is all.
No. Tanker is just a written test.
No, you cannot.
Yes. If it requires a tanker with an unrestricted CDL, so it does with a permit, as well.
You will need a Class B CDL with tanker endorsement.
X is a combination of Hazmat (H) and tanker (N) endorsements.
HME won't be seen on a CDL - the endorsement for hazmat on a CDL is H, or X if it's in conjunction with a tanker endorsement. HME is often used as a shortened form of "hazmat (or 'hazardous materials') endorsement".
If the vehicle requires a CDL in service, it'll require a CDL for the test drive.
The X endorsement is a combination of two endorsements - Hazmat (H) and tanker (K).
Yes. Tank trucks require a tanker endorsement, and the tanker endorsement can only be put onto a CDL. A permanently mounted tank requires one (the regs don't specify a minimum capacity), as do portable tanks of more than 1000 gallons.
The CDL test, which stands for Commercial Driver's License, is a test which allows one to drive large vehicles. If you are planning to work in a field involving driving large vehicles, you should take the CDL test.
Being someone with a CDL, you should know there is no actual air brake endorsement on a CDL - you get a restriction barring you from operating air brake equipped commercial vehicles. You need to take and pass the written air brakes test, and you need to conduct a road test in a vehicle equipped with air brakes. Then you can have the restriction removed from your CDL.
One can get practice CDL test questions on several websites. These websites include CDL's official website, which is the most trusted website to find CDL practice questions.