From what point on the basket do you measure a high school three-point line?

The line is measured from the CENTER of the basket using a plumb bob.

In the U.S., college and high school rules for both men and women specify a distance of 19 feet, 9 inches (6.02 m) from the basket. This line lies at the same distance from the basket as the top of the key, so the 3 point line coincides with the top of the key at the center point.


https://en.wikipedia.org/wiki/Three_point_line#Rule_specifications


http://www.basketball-goals.com/basketball%20court%20dimensions.htm#3point