Although having said that the draft simplified Laws doesn't cover it - perhaps we can gain a clue
The draft law book does say
INFRINGEMENT/STOPPAGE
knock-on or throw forward, apart from at a lineout.
LOCATION OF SCRUM
n the scrum zone at the point closest to the place of infringement
WHO THROWS IN
The non-offending team
The 'scrum-zone' is undefined in this draft, but we can assume it means the area bounded by the four 5m lines.
The inferences perhaps we can draw is that
- all knock ons (other than at a lineout) are treated just the same
- there is nothing particularly special about a knock on in goal compared to any knock on anywhere else outside the scrum zone
- and so after such a knock on, just like any other knock on, advantage can be played in the normal way.
Anyway - it will certainly be interesting to see the final version. We're going to have fun!