Answer
$$\frac{1}{2}(\ln (\sin x))^2+c.$$
Work Step by Step
Let $u=\ln (\sin x)$, then $du=\frac{\cos}{\sin x}dx=\cot x \ dx$ and hence we get
$$\int \cot x \ln(\sin x)dx= \int udu=\frac{1}{2}u^2+c \\
=\frac{1}{2}(\ln (\sin x))^2+c.$$
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