If you are driving 24000 lb truck pulling a trailer and cargo of 12000 pounds do you need a cdl and if so what class?

If it's a vehicle being operated on a commercial basis, then yes, that combination will need a CDL. Commercial vehicles and combinations in excess of 26,000 lbs. Gross Vehicle/Gross Combination Weight Rating require a CDL. For that combination, you would need a Class A CDL (combinations over 26k GCWR with a trailer in excess of 10,000 lbs. GVWR).

If the vehicle is a registered farm vehicle, it does not require a CDL if the following criteria is met:

• It is registered and plated as a farm truck
• It is operated by the farmer, immediate family members of the farmer, or direct employees of the farmer (direct employees are W-2 employees, not 1099 employees)
• It is used only for the purposes of that farm, and not hired out to provide services as a third party (which is illegal to do with a farm truck, anyhow)
• It remains within a 150 miles radius of the farm

If the vehicle is a registered recreational vehicle, and is not operated on a for-hire basis, no CDL is required.

Even if the vehicle falls under an exemption from CDL requirements, individual states may impose their own licencing requirements for non-CDL vehicles and combinations with a Gross Weight Rating of more than 26,000 lbs. As I'm not privy to know which state you're operating in, you'll have to inquire with your state's DMV.