Q.Yucca tree
I know how to propagate a Yucca tree, but how can you get the tree to make these offshoots (pups)? I have four Yuccas which are growing very strongly and producing pups, except one, and I want to induce it.

I've not tried this myself, and I don't know any way to force "pupping" unless it would be to cut off the growing top of the yucca. However, I have heard of agaves that start to pup actively when newly rooted cuttings are brought inside to overwinter. These of course are potted.