Okay, well I'm going to assume that you have a timid nature and are EV trained 252 in Special Attack for your Nidoking if you're calculating the kind of damage you'll do.

This being how damage is multiplied..

Damage = ((((2 * Level / 5 + 2) * AttackStat * AttackPower / DefenseStat) / 50) + 2) * STAB * Weakness/Resistance * RandomNumber / 100

- Serebii So lets do some math.

Now let's use this formula. Say I wanted to see the effectiveness of Umbreon's bite on an Espeon (I'm using neutral-nature maximum stats for this example). The pokemon are both level 100. Bite's attack power is 60. Lets say the Random Number is 100. Now let's plug in all the numbers:

Damage = ((((2 * 100 / 5 + 2) * 219 * 60 / 289) / 50) + 2) * 1.5 * 2 * 100 / 100

Damage = ((((42) * 219 * 60 / 289) / 50) + 2) * 1.5 * 2

Damage = (((1909.6) / 50) + 2) * 1.5 * 2

Damage = 44.9

Damage = ~45

So, like they did it with Umbreon, you can input your Nidoking's stats, and see what kind of damage he would do to different defense leveled pokemon.

I would, but I really don't feel like doing the math right now.

And as far as his attack, it would be 269 + 63%, which hovers around 410.