(x÷(y÷z))÷((x÷y)÷z)
also the variables are not specified.

The answer is:  z² .

Given: (x÷(y÷z))÷((x÷y)÷z) ;  without any specified values for the variables; 

we shall simplify.

We have: 

(x÷(y÷z))  /  ((x÷y)÷z) .

Start with the first term; or,  "numerator":  (x÷(y÷z)) ;

x  ÷ (y / z) = (x / 1) * (z / y) = (x * z) / (1 *y) =  [(xz) / y ] 

Then, take the second term; or "denominator":

((x ÷ y) ÷z ) = (x / y) / z =  (x / y) * (1 / z) = (x *1) / (y *z) = [x / (zy)]

So (x÷(y÷z))  /  ((x÷y)÷z)  = (x÷(y÷z)) ÷  ((x÷y)÷z) =

 [(xz) / y ] ÷ [x / (zy)]  = [(xz) / y ] /  [x / (zy)] =
                                                                    [(xz) / y ] * [(zy) / x] ;

                               The 2 (two) z's "cancel out" to "1" ; and
                                  The 2 (two) y's = "cancel out" to "1" ; 

And we are left with: z * z = z² .  The answer is:  z² .