I found a free online WTX sandbox you may use to develop a simple COBOL copybook to XML map. It apparently only provides 4 hours of access but that should be enough to learn some basics. I'm not certain if you can do anything besides the exercise.
Exercise: Transform a text document into XML using WebSphere Transformation Extender
In this exercise, you will use the COBOL copybook importer to automatically create a WebSphere Transformation Extender type tree, which you will customize using the type designer. Then you will create a map that transforms into an XML document the simple text document you imported into your type tree.