Assuming you are referring to the AGA cooker, there is no one answer to this question as the temperature of different parts of the AGA cooker can vary depending on how it is being used. However, in general, the hottest part of an AGA cooker is likely to be the oven door, which can reach temperatures of up to 500 degrees Celsius when in use. Other parts of the cooker that can become hot include the hotplates and griddle, which can reach temperatures of up to 260 degrees Celsius, and the boiling plate, which can reach temperatures of up to 100 degrees Celsius.