If you have access to 3ds Max, you should be able to import JT files as 3ds Max Body Objects, support for the JT format is provided by Autodesk DirectConnect. You might also find some dedicated 3D model converters like the Babel3D that should be capable of jt to 3ds conversion.
Open JT file Open 3DS fileAn online CAD conversion service
A commercial online CAD converter
A 3D CAD translation software