Do I cut the end of the root at and angle or straight across
Rooting Desert Rose From a Broken Limb.
Certified GKH Gardening Expert
If it still has a root attached, then you do not want to cut this off. This will give you a kickstart on the process, instead of waiting for it to regrow a root that has been cut off. So I would not cut the root off at all.
If, in fact, you meant the stem and not the root then you will want to cut this at an angle. This article will give you more information: https://www.gardeningknowhow.com/ornamental/flowers/desert-rose/desert-rose-propagation.htm