Assuming the truck has a true automatic transmission it will depend on the truck. Should be marked or check the owners manual. More importantly trucks that a school or company paid training use will have manual or automated manuals and will not utilize ATF.
The cdl manuals include many items that may not be on all vehicles. Your pretrip will be graded based upon the vechicle you bring to the test. By that time your school will have shown you what you need to know.
Don't overthink this.
A CDL is required to drive any of the following vehicles:
Unless it is your truck, and since you are asking I will assume it is not, be very careful. Overfilling a transmission is bad for the transmission and a pain to drain. Very little chance of it being low unless you see an actual transmission fluid leak. There is also a special procedure as far as warming to temp to check it correctly.
Does not get checked.
Should be changed every 500,000 miles. Same thing with the differentials.
Check this out:
Pre-Trip Inspection - My Way! A Must See!
A Trucking Truth classic.
A pre-trip inspection is a thorough inspection of the truck completed before driving for the first time each day.
Federal and state laws require that drivers inspect their vehicles. Federal and state inspectors also may inspect your vehicles. If they judge a vehicle to be unsafe, they will put it “out of service” until it is repaired.
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Also, how would you check the ATF level?