How do I know whether I’m fire, water, wood or metal element?

If the last number in your birth year is 0 or 1 then your element is metal.

If the last number in your birth year is 2 or 3 then your element is water.

If the last number in your birth year is 4 or 5 then your element is wood.

If the last number in your birth year is 6 or 7 then your element is fire.

If the last number in your birth year is 8 or 9 then your element is earth.

Of course, this might not be accurate if you were born in another year, but before CNY (like how those born this year before CNY are Rat and not Ox). So to be sure, you can check the Table of the Sixty Year Calendar.