Very gently. A motorcycle battery can't take as much charging current as a car battery, so you need to use the lowest setting on your charger.
No, not if the motorcycle is wired for a 6 volt system. This must be a very old motorcycle.
Charge it with a 12 volt battery charger.
Motorcycle batteries may be 6 volt rather than 12 (check this) and if they are 6 volts, switch your battery charger to 6 volts or you may damage the battery.
No
No.
Usually 12 Volt
Unless it's an old vw bug, cars usually run on a 12 volt dc system nowadays. Motorcycles often run on a 6 volt dc system. Different systems require different charging voltages so you won't ever be able to charge a 12 volt car battery from a 6 volt motorcycle battery charger as the output voltage would be way too low. However, if you can set the battery charger's output to give either a 6 or a 12 volt output, then you must always remember to set it to 12 volts if you want to use it to charge a 12 volt car battery.
No, a 12 volt charger will overcharge a 8 volt battery and destroy it.
no it can't
No it will not work
No, the battery is DC not AC.
If you are asking the question, can you charge a 6 volt battery with a 12 volt charger, the answer is no.