By running the Contract Register report, you can find a variety of information pertaining to your workers' contracts. This includes rates, timesheet approver, billing contact and the worker's profile - PAYG or Pty Ltd.
Ensure that you look for the Profile column when viewing the report. If a worker is being paid via their TFN, this will show PAYG. If a worker is being paid via their own company this will reflect Pty Ltd.