I suspect the method will vary based on the model of printer you are using, and that you would need to refer to the printer documentation to see what it uses.
My expectation is that you have to end up creating a front-call
http://4js.com/online_documentation/fjs-fgl-manual-html/#c_fgl_frontcalls_user_ext_gma.html and following the steps here
http://4js.com/online_documentation/fjs-fgl-manual-html/#c_fgl_JavaBridge_gma_packaging.html to include the front-call in your Genero Mobile package.