One way is to have tracking groups and tracking points tied to the business data you want to track along with the logged in users and then use Scoreboards and Reports to generate dashboards for audit trail.
Another way is to have database driven audit logging e.g. trigger based or end data and start date every piece of data with users, but this means you will need intermediate saves in your Process after every Human Task.
If you have advanced version Business Monitor is the ideal solution.