How can i propagate this cutting piece of agave?

Let it heal over first. then try to root it by placing it in gritty well drained soil.. It may or may not work..... some do and some don't......

http://homeguides.sfgate.com/propagation-growing-planting-agave-65474.html

Ditto on what johnavallance82 said. Be sure to let it heal over prior yo lightly placing in sandy well drained soil. Wishing you luck ♥

Place it in a small clay pot of sand about two inches deep is good. These plants require little water or nutrients so water only when dried out and feed once with a weak common fertilizer only after roots have developed then transfer to permanent pot with average good draining soil. Feed twice a year and keep in bright but not direct sunlight.

you can also get a rooting hormone to use but wait till its healed but not totally then put in sand away from direct sunlight.