The best way to start Euphorbia's (which is what Crown of Thorns are), like stated above, cut, let the cut heal over (takes a few days). Don't let dry out in open sun. I keep mine inside spray misted lightly. Soil on dry side but not totally dry. Kept in bright light not direct sun. In about two weeks they start to require more misting. When new growth shows you can begin watering them but very lightly. They can be given more sun light by now.
Not good to just cut up a large plant and expect all the cuttings to take. I would cut only the top growths. Let heal, take more cuttings when new growth fills in what you took. This will become a continuous project, not one big cutting and then reward of all the cuttings taking.
When trading with friends. That is mostly all you get is a stem cutting. Which is all you really need.
Stush
