No, the onions would not be safe to eat. You should never eat any food that has been left sitting out for 48 hours.
As long as the food was cooked properly the first time and proper storage precautions were observed, then there is no set temperature that must be reached in order to safely reheat it. Warm to whichever temperature you desire in order to enjoy it.
Pork should be cooked to an internal temperature of 145F (63C) to ensure it is cooked thoroughly and safely.
The minimum internal temperature for eggs to be safely cooked is 160F (71C).
The recommended internal temperature for a meatball to ensure it is safely cooked is 160F (71C).
The recommended internal temperature for cod to ensure it is safely cooked is 145F (63C).
The recommended internal temperature for meatballs to ensure they are safely cooked is 160F (71C).
A ham needs to reach an internal temperature of 145F (63C) to be safely cooked.
The recommended internal temperature for chicken to ensure it is safely cooked is 165F (74C).
Cook a ham to an internal temperature of 145F to ensure it is cooked thoroughly and safely.
The recommended internal temperature for a chicken burger to ensure it is safely cooked is 165F (74C).
The recommended internal temperature for a pot pie to ensure it is safely cooked is 165F (74C).
The recommended internal temperature for rotisserie chicken to ensure it is safely cooked is 165F (74C).