Which CDL license do I need to drive a Triaxle dump truck?

It would require a Class B CDL, without an air brake restriction (there is no air brake endorsement - only a restriction if you don't pass the written air brakes test and perform your pre-trip and road tests in a vehicle so equipped). You would only need a Class A if that vehicle was going to tow a trailer with a GVW in excess of 10,000 lbs.