Answer
$\dfrac{1}{z^{4}}$
Work Step by Step
Using the laws of exponents, the given expression, $
\dfrac{z^{-6}}{z^{-2}}
$, is equivalent to
\begin{array}{l}\require{cancel}
z^{-6-(-2)}
\\\\=
z^{-6+2}
\\\\=
z^{-4}
\\\\=
\dfrac{1}{z^{4}}
.\end{array}