All of CB profile data is contained in _comprofiler table. You can do whatever you like with it including move it to Joomla fields if so desired.

Is there a reason you need to do this? CB is capable of rendering Joomla fields so you can instead move your Joomla fields to CB and let it render both perfectly fine. When CB renders a Joomla field it also stores it to Joomla user profiles instead of _comprofiler so if you need the field to exist in both CB and Joomla then you'd simply use a Joomla field type.