What energy is used in a pen?

The power of pressure transmuted from your hand to a piece of paper.

Gravity, I think is what you’re looking for. There’s no internal sort of energy, it’s utilizing outer forces.
Here’s a better explanation of what is going on if you’re interested.

I’m looking at a pen sitting on my table right now, and it’s not using any energy. It’s just sitting there. If I pick it up and write with it, I’m converting the chemical/metabolic energy of my muscles into the kinetic energy needed to move the pen from one end of the line to another. Some of that kinetic energy will get converted into thermal energy by the friction of the tip of the pen rubbing against the paper.

Do you mean Embodied Energy? That would depend on the specific make and model of the pen to which you refer. You would probably have to contact the manufacturer to get that information.

Actually, it’s not really gravity. Pens rely on the electromagnetic force on the molecular level. The effect is based on capillary action or adhesion and occurs because of inter-molecular attractive forces between the liquid and solid surrounding surfaces, see

http://en.wikipedia.org/wiki/Capillary_action