exif information not available on jpg when exported from a nef fille with RAWTHERAPEE

I just checked and you are using the old 5.8 version, which, indeed, has this issue.

This problem is already solved, though.

I would strongly advise you to use one of the latest development versions until the new release comes available. These development versions have many new/fixed features, added support for new camera types and solve a lot of issues that are present in the stable, but very old, 5.8 version.

Have a look here for the download that suits your OS:

BTW: Welcome to Pixls!