UGS offers a command line executable called TxJT2co. It is not a standalone application; it is part of CAD Translator module which comes on top of Robcad or Tecnomatix.
This application converts *.jt assembly or *.jt part to a RobCAD/Technomatix .co file. The translator contains flags that enable you to select the *.jt file for conversion, the destination location, and several optional flags to customize the output according to your needs.