Mullens is listed as the QB2 on the team’s unofficial depth chart, so probably him.
But even if Hall is the backup they might still think Mullens is the better QB, but also think that Hall can execute a Dobbs gameplan better than Mullens can. In that situation Mullens would probably start if Dobbs goes down but Hall would finish out any games Dobbs started.
It’s also possible that the actual depth chart has Hall ahead of Mullens.
So the short answer is who knows, and it doesn’t really say anything meaningful about what the team would do if Dobbs gets hurt or benched.
Mullens is listed as the QB2 on the team’s unofficial depth chart, so probably him.
But even if Hall is the backup they might still think Mullens is the better QB, but also think that Hall can execute a Dobbs gameplan better than Mullens can. In that situation Mullens would probably start if Dobbs goes down but Hall would finish out any games Dobbs started.
It’s also possible that the actual depth chart has Hall ahead of Mullens.
So the short answer is who knows, and it doesn’t really say anything meaningful about what the team would do if Dobbs gets hurt or benched.