Here are some places to check when searching for your TFN:
Login to your myGov account
Payment summaries from your employer
Lodged income tax returns (this is would be from the ATO)
Previous super statements
Ask your accountant
Or you can call the ATO, they will be able to help you locate your TFN.
Student Super is authorised under the Superannuation Industry (Supervision) Act 1993 to collect, use and disclose your Tax File Number (TFN). By providing your TFN, you give Student Super permission to use your TFN for superannuation purposes, which includes creating and administering your account and actioning your rollover requests. It is not compulsory to tell us your TFN, however if you don’t do so, your before-tax contributions and withdrawals are taxed at a higher rate and we can’t accept after-tax contributions from you, and we will not be able to help you find your existing and lost super.