"Locating a point" doesn't mean much to me.
If you want to trigger some action when the sine wave reaches the value of 1.5 volts, that can be done using the Arduino built in analog comparator. It compares the input voltage to a reference voltage that you define, and provides a signal for input less than or greater than the reference.
Alternatively you can measure the input voltage with the analogRead function, but you are limited to relatively low frequencies for the input sine wave.