This dipstick is usually located on the driver's side of the engine compartment, near the back of the engine, but its exact position can vary slightly. It might be a long dipstick that's hard to see, so you might need to carefully feel around in that area to find it. It often has a bright colored handle or marking to distinguish it from other dipsticks.
Important Note: Checking the transmission fluid level requires the engine to be running and the transmission to be at operating temperature. Consult your owner's manual for the specific procedure, as improperly checking the level can give inaccurate readings. Adding fluid is also a specific procedure and shouldn't be done lightly. If you're unsure, it's best to have a qualified mechanic perform the check and service.