You will find this amount in your previous tax return (i.e. 2016 tax return) submitted. If you have a copy of the return, look on schedule 17 of the return to see what the total taxable earning were.
If you do not have this amount, just enter NIL and continue for the time being - however it is vital for a complete return, to enter the correct amounts.
If you used TaxTim in the previous year, just let us know, and we can provide you access to the previous return for viewing.
We also received several requests that the information should pull through automatically from the previous return.
We will develop the functionality as soon as possible after the close of this 2017 tax season.