Concept:
Absolute value functions are continuous everywhere but may fail to be differentiable where the expression inside modulus changes sign.
For:
\[
|g(x)|
\]
non-differentiability occurs at points where:
\[
g(x)=0
\]
or where \(g(x)\) itself is non-differentiable.
Step 1: Analyze the given function carefully.
Given:
\[
f(x)=|2-|x||
\]
We first examine the inner modulus:
\[
|x|
\]
which is not differentiable at:
\[
x=0
\]
Next consider:
\[
2-|x|
\]
This becomes zero when:
\[
2-|x|=0
\]
\[
|x|=2
\]
Thus,
\[
x=\pm2
\]
At these points, the outer modulus changes sign.
Step 2: Determine differentiability.
The function is continuous everywhere because modulus functions are continuous.
However:
• At \(x=0\), \(|x|\) is non-differentiable.
• At \(x=2\) and \(x=-2\), the outer modulus introduces sharp corners.
Hence the function is not differentiable at:
\[
x=-2,\;0,\;2
\]
Therefore the required set is:
\[
\boxed{\{-2,0,2\}}
\]