According to the Heisenberg uncertainty principle, if the position of a moving particle is known, what other quantity cannot be known?

The correct answer is velocity.

A law in quantum mechanics, which restricts that how precisely one can determine the two associated variables is known as the Heisenberg uncertainty principle. Heisenberg illustrated this using something known as the observer effect that illustrates that very act of determining one value influences the other, and thus, presents certain kind of uncertainty.

Heisenberg uncertainty principle, also known as uncertainty principle postulated by the German physicist Werner Heisenberg, that the velocity and the position of an object cannot be determined exactly at the similar time, even in theory.