The modulus of $ z $ is:
$$ |z| = 2 \sqrt{ 3 }$$To find modulus of a complex number $ z = a + bi $ we use formula:
$$ |z| = \sqrt{a^2 + b^2} $$In this example we have $ a = -\sqrt{ 6 } $ and $ b = -\sqrt{ 6 } $ so:
$$ \begin{aligned}|z| &= \sqrt{ \left( -\sqrt{ 6 } \right) ^ { 2 } + \left( -\sqrt{ 6 } \right) ^ { 2 } } \\[1 em]|z| &= \sqrt{ 6 + 6 } \\[1 em]|z| &= \sqrt{ 12 } \\[1 em]|z| &= 2 \sqrt{ 3 } \\[1 em] \end{aligned} $$