You'd need 0.500 ML in order to precipitate that much magnesium from your solution.
Start with the balanced chemical equation for this double replacement reaction
This reaction will form sodium chloride, a soluble salt, and magnesium hydroxide, an insoluble solid that will precipitate out of the solution.
So, you know that you're dealing with a 1.00-ML, 0.0500-mol/L solution of magnesium chloride.
Use the solution's molarity to determine how many moles of magnesium chloride you have
Use the aforementioned mole ratio to determine how many moles of sodium hydroxide you'd need
Since you know the molarity of the sodium hydroxide solution, you can determine the volume you'd need by
This is equivalent to having
SIDE NOTE Here's how the net ionic equation looks like for your reaction