What is the kinetic energy of a pendulum at the side compared to at the bottom of the “path”

When it is at the top of its path (the side), the total energy is equal to just the potential energy since it isn't moving. This is m*g*h, where m is mass, g is acceleration due to gravity (~9.81 m/s/s), and h is the height above the bottom of the path.
At the bottom of the path, all the energy is now converted into kinetic energy. This is equal to the potential energy, and is also equal to 1/2 * m *v^2, where v is the velocity at the bottom of the path (which is all in the horizontal direction).