Apogee (or maximum) of a curve on a given axis? Or closest point on a curve to a plane?

Is it possible to find the maximum of a curve? Or the closest point on a curve to a given plane? I know how to do this with calculus...

I thought Curve CP might do it, but I don't have a reference point so much as a plane. I tried sticking a plane into the point input of Curve CP, but it just used the plane's origin.