Answer
{1}
Work Step by Step
For all positive numbers $a$, where $a\ne1$, and all positive numbers $x$, we know that $y=log_{a}x$ means the same as $x=a^{y}$.
Therefore, $log_{12}x=0$ means the same as $12^{0}=x$.
We know that $x=1$, because $12^{0}=1$.