Your Yucca has stems that can be pruned at any point along them. New growth will then emerge starting just below the pruning cut and grow upward from there. In the closeup photo you provided, I suggest pruning just above the new shoot that has already started to emerge. Mostly, it is a matter of how tall you want the plant to be after pruning and how you want it to look.
Using tip cuttings with about 6-8 leaves and 6 inches of bare stem below those tip leaves is the best way to propagate it. The tip cuttings can be rooted fairly easily in plain water; inserted in the base of the existing pot; or in their own small pots filled with damp porous potting mix. Rooting hormones are not necessary. Although the Yucca stems are quite thick, they are not very woody, so air layering is not necessary, as you might expect.
The other plant is commonly called Dracaena 'Janet Craig,' not Corn Plant, which has yellow striped leaves. It can also be pruned back and propagated in the same way as the Yucca.