Awhich layer of the earth will jaron's
tunneling machine experience the
greatest heat and pressure?

The inner core

Explanation:

Well, Jaron's tunneling machine would find it quite impossible to even penetrate the crust.

Our dynamic earth is arranged in concentric layers with each shell at varrying physical state and chemical properties.

As we go down the earth, the temperature and pressure increases significantly. The innermost layer of the erth is the inner core and it is expected that the temperature and pressure here should be the greatest. The pressure in the inner core is so great that the materials that were supposed to be in molten form exists as solid in there.