Does $-x^2$ does mean $-(x^2)$ or $(-x)^2$? When I see something written as:  $-x^2$ does it mean $-(x^2)$ or $(-x)^2$ ?

..and why? I can't apparently apply a streight PEMDAS rule to it
If it helps, think of it as $0-x^2$.  The Exponent wins first, then the Subtraction.  Hence it means $-(x^2)$.
The products have always prioprity upon the sums. So $-x^2 = - x \times x = - (x^2)$.