line between tow points on tow surfaces

Please, I need to create line between tow points on tow surfaces whereas the line length should be as minimum as possible as follow:

1- Enter (x,y) for the first point (input).
1- Pick the point on the first surface.
2- Find the nearest point on the next surface.
3- Create the line.

I was trying to find that in this poor documentation with no luck.

Thanks in advance,