From the Kmart Facebook Page in a recent comment thread, and I confirmed in private message afterwards:
We offer a Pensioner Discount Day on the first Wednesday of every month. The 5% discount is available for Commonwealth Government Pensioner Concession Cards or Commonwealth Government Department of Veterans Affairs Health Cards only. Commonwealth and State Government seniors cards are not accepted for this offer.
The offer is available in-store only, at all stores nationally.
From other private groups and discussions it seems hit & miss whether the staff member you encounter will know of this offer, but you can advise them that there should be a dedicated 'pension discount button' on their screen that says 5% off. Worst case scenario, you can show them the comment from Kmart directly.
I'm actually quite mad that Kmart do not make this known at all, but they do provide the information IF YOU ASK. I get why, but it still leaves a bit of a bitter taste in my mouth.
How does this compare with staff discount?