The low poly needs UVs, the high poly doesn't if you're using polypaint. You'll need to turn off the "ignore per-vertex colours" option in XNormal if you are using polypaint though.
Just to outline it: 1. Export your UV'd low poly and your high poly thats polypainted as .obj (UVs on HP don't matter). 2. Plug both into xNormal in their respective sections and check "Bake highpoly's vertex colors" box for baking - make sure to uncheck "Ignore per-vertex-color" on your high poly. 3. After you bake that,…
afaik, you wouldn't need to involve Zbrush in the high poly - low poly process at all. My take on the workflow would be export the Zbrush high poly sculpt as an obj, export the low poly in the relevant file format, and then using XNormal place the high poly sculpt in XNormal's high poly object section, place the low poly…