How do you find the unit vector having the same direction as vector v = –12j?

$\hat{v} = - \vec{j}$
$\hat{v} = \frac{\vec{v}}{| \vec{v} |}$
$| \vec{v} | = \sqrt{{\left(- 12\right)}^{2}} = 12$ (this is the norm or length of the vector so we take the positive root.
$\hat{v} = \frac{- 12 \vec{j}}{12} = - \vec{j}$