Hi Cyna, Extract from ATO website - "Superannuation guarantee - New rules are being introduced by the government with the intention to not require super guarantee to be paid on additional payments that are made to employees as a result of JobKeeper payments. We will update this information once legislation or regulations are in place." The jobkeeper portion of the payment is not subject to super.
If they are working some hours you should record that as a normal wage (say $300) and then the top up is the additional amount over and above the $300. Say $450 if paid weekly or $1200 if paid fortnightly. No SG is required to be paid on the top up, but obviously you can do so if you wish