I have sodium hydroxide, I want elemental sodium. I saw one video in which he used very high voltage current source. Can I do that with a 9v battery?

How long have you got ?

Sodium reacts with water to form sodium hydroxide and hydrogen gas



You will never get elemental sodium using electrolysis. The minute it is made, it will react with water and become hydrogen and NaOH again. Sodium is stored in oil.