I have the exakt same issue. Using habpanel with openhab2, i can put the scripts in the openhab2 directory as explained in the Reader and the Demo widget is displyed correctly.
However Wien im using the iobroker habpanel, I don't know where to put the scripts and how to Reference them,. Openhab habpanel and iobroker habpanel run on different ports. So where is the correct location for the Java scripts?