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.
To obtain a tanker endorsement, you must first hold a valid commercial driver's license (CDL). Then, you need to pass a written knowledge test specific to tank vehicles, which covers topics like safe handling and transportation of liquids. After passing the test, you may also need to demonstrate practical skills during a driving test, depending on your state’s requirements. Finally, you’ll pay any applicable fees to have the endorsement added to your CDL.
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.
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.
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.