Answer
{$(x,y,z) | x^2+y^2+z^2\leq 1$}
Work Step by Step
We are given that $f(x,y,z)=arcsin(x^2+y^2+z^2)$
The function $f(x,y,z)=arcsin(x^2+y^2+z^2)$ represents a trigonometric function and we know that $\sin x$ lies in between -1 and +1.
Thus,
$ -1 \leq x^2+y^2+z^2\leq 1$
Or:
$x^2+y^2+z^2\leq 1$
Hence, {$(x,y,z) | x^2+y^2+z^2\leq 1$}