Vladimir,
I think the best graph for this purposes is the XY graph, but actually the graph you are going to use is going to depend in which kind of data are you plotting so you may better have a decision on which kind of data you are going to be handling, then you decide which graph is best for this purposes and then we can try to work in to see how to get the Y and X points from it. Also it seems a little confuse for me to know why would you like to get this values out of a graph if for a first instance you have to input this values to it, so you don't have to go through getting values from a graph if you already have them before going into it, makes sense?
However, I attached here an example with an XY graph, it calculates 100 points of a sine wave,
plots it and then it gets the data from the graph in two separate arrays one for the Y values and one for the X values, look for more details inside the example.
Good luck!....
Nestor Sanchez
Applications Engineer
National Instruments
Nestor