I live in zone 5.

Coupla years ago, I got some plumeria stems, thinking they were evergreen in their native habitat.
For 12 months I tried to grow them inside, in too small pots.

Then after I learned some, I transplanted them into larger pots and set them out in the warm summer of 2014.
I brought those inside for the winter, in my basement, with some light but maybe not enough.
They are completely bald now.

I since learned that they do go dormant.

SO I repotted them, leaving about 10" below and 3" above int soil.
They all lost their leaves over the winter but I now understand that they go dormant.
Today I moved them back out to the deck, bald.

Q: do I want to add soil on TOP of what's there, in the supposition that they will root from the stem (like tomatoes) OR do I want to unpot them , add soil below, and put them back.

Yes you are right in your time zone they are still dormant.

The stem will not root only the bottom part. When you reported it did you notice any roots? If you have a picture that would help if you can post it here.

Depending on the length of the cutting I would only bury 2 to 3 inches. I keep the soil more to the dry side while still in dormancy to avoid root rot. Plumerias do not like wet feet. I also keep them in a warm sun when the weather is always above 50+. Then once 3 to 4 sets of leaves would open up I resume normal watering.

Thank you.
That was really helpful.

You are welcome . If the soil looks too dry (especially in our time zone) I would mist the stem or wrap a wet paper towel and Mist the top soil just enough to prevent the stem from dying out.