If you either cannot recall your TFN or alternatively, are unsure whether you do in fact have one, it is best to call the ATO directly to gather the correct information. Unfortunately we do not have the authority to call on your behalf as the ATO will need to verify your identity and ask personal questions of which we have no knowledge.
You can call the ATO on 13 28 61 Mon-Fri 8am-6pm to be advised of your TFN.
Your TFN will usually feature on a range of documents you may have in your possession such as a payment summary from an employer, an income tax assessment from years past or any written communication from the ATO.
If you are located overseas and need to contact the ATO regarding this matter you can do so by calling +61 2 6216 1111 8am-5pm Australian weekdays.
N.B. Remember that applying for an ABN without a TFN means that the ATO will hold your application under manual review for 28 days.