I would like to see a solution for this as well. I used to be able to record this information and get a report of that, very easily in Erwin.
It is very hard to do both of these in PD.
PD likes to have the source model open in Workspace for it to even show previously created source to target mappings. In Erwin, it just imports the table structures from the model and then there is no connection to that model anymore. You can then see an extra Data Source tab attached to each columns definition where you see this source model table and column name to pick from. A report in CSV format is then easily created from this information.
This has been valuable information for me when supporting the Data warehouse models I created. I first lost of of this info in model conversion. And second, no easy way to create and report on this in PD 16.1 that we use.