Answer
$$\frac{1}{20}.$$
Work Step by Step
Assume that $\csc\theta =\frac{20}{1}$, then by solving the triangle, we have:
$$\sin\theta=\frac{1}{20}.$$
Now, since $\theta =\csc^{-1}20 $, we have
$$\sin(\csc^{-1}20 )=\sin\theta=\frac{1}{20}.$$