Details of salary sacrifice payments should be included on the payment summary provided by your employer.
If you have a copy of the payment summary, the amount should be listed under the "reportable employer superannuation contributions" heading.
Otherwise go to MyTax, access your tax return, select "view" next to the "Income statements and payment summaries" heading, then hit the down arrow next to the tax withheld amount for the employer. You should then be able to locate the "reportable employer superannuation contributions" heading.