Today I updated goz plugin for blender 2.8. You can grab it from here (press download in top right).
The plugin supports exporting:
-polygroups (aka. vert weights)
-polypaint (aka. vertex colors)
-uv
After installation use those buttons to import, export files to zbrush:

If you have problems with setup, it may be that your zbrush GOZ installation is broken.
You can re-install GoZ, make sure ZBrush and Blender are closed. Now you go to your ZBrush folder:
C:\Program Files\Pixologic\ZBrush 2018\Troubleshoot Help\
In there should be a file called “GoZ_for_ZBrush_Installer_WIN.exe”, right click and run with admin rights, follow the installer through.
If you haven’t, go can now install GOZ for blender now by following readme in goz for blender zip file.
Now open ZBrush, go to Preferences – GoZ – force reinstall. Locate your Blender 2.8 path.