To simplify the expression \( \frac{\ln x \cdot \ln y}{\ln z} \), we can use the properties of logarithms. However, the current expression doesn't naturally reduce to a single logarithmic form without any additional context or constraints.
The expression \( \frac{\ln x \cdot \ln y}{\ln z} \) does not fit typical logarithm properties that allow for further simplification into a single logarithmic term. Thus, the correct answer is:
This expression cannot be simplified.