Hi, the normal workflow is you need to create the UV's before skinning the Character.
But there is a work around using the transfer attributes tool (Select 'component' in the sample space options)
Unfortunately because transfer attributes still needs to be connected for your new U'Vs to stick to the geo it will make the rig heavy to animate and you can't change its order in the inputs stack (thanks Maya!) so you need to do this fix:
Every object has a “shape orig” node which represents what an object was before it was deformed.
1. Select your rigged object, in the hypergraph hit options/display/ hidden nodes & shape nodes
2. You’ll see a hidden node which is your Orig node, or what your object was before rigging.
3. In the orig node’s attribute editor under object display, uncheck ‘intermediate object’
4. Your Orig node is now accessible.
5. Apply your UV transfer attributes to it – then delete it’s history.
Hope this helps
P
Phinnaeus O'Connor Ltd
3D Animation for TV and Film