This will depend on the size of the 12 v battery.
Yes but you will deplete the battery quickly.
if it is any think over 1 volt it is not a cell battery it is just a 6 volt battery if you had a 1 volt then it would be a cell battery
No, it will overcharge the 6 volt battery.
The battery is a 12 volt.
The battery cannot be removed quickly! Inductance of the wiring stores energy and keeps the current flowing and decaying smoothly. There will be an opposite polarity, higher voltage pulse on the battery terminals, limited by the circuit capacitance only.
1 volt battery does not exist.
Charge it with a 12 volt battery charger.
No, you cannot charge an 8 volt battery with a 6 volt charger. The voltage of the charger must match the voltage of the battery.
Impossible to do with a single 6 volt battery.