I am assuming you have the equation used for plotting. You can feed the value “x=0” in the function to get the value of “y” and vice versa and store these values in variable “pos1” and “pos2”. Without having the values for both “x” and “y” you cannot obtain the DataCursor on the plot.
I am attaching a slightly modified code for your given code with which you can obtain DataCursor at any point of your choice. I have commented few lines that are not needed and changed few lines of code for updating DataCursors.