It appears that .jnb and .spw files are used by SigmaPlot graphing software, so some sort of conversion or data transfer is likely. Considering the support for SigmaPlot's format is pretty limited in 3rd party programs, you will have to use the original tool only.
Convert SigmaPlot workbook to SigmaPlot worksheet file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert jnb to spw on Windows
A graphing software
Convert from jnb file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.