CAD programs like Solid Edge or NX support both JT and PRT CAD formats and thus could possible perform conversion between them. Might require some intermediate conversion step between them however, like using the common DWG.
Convert JT Open CAD 3D model format to CAD 3D part or component.
We found 4 software records in the database related to .jt to .prt file format conversion.
Microsoft Windows software - convert jt to prt on Windows
A feature rich 3D CAD software by Siemens
Convert from jt file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned jt to prt. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A CAD converter with huge format support
A 3D CAD, CAM, and CAE designing software by Siemens
Set of 3D CAD/CAM/CAE design tools from PTC