Re: Graph BuilderInstead of dragging your Before-After variable to the X-axis, where it nests the variables, drag it to the Group X location above the graph. That will automatically put a line between the Before and After groups.
Re: Graph BuilderNo way just add line?? (I don't want to redo fig.)
P.S. So, I'll have to draw line
Re: Graph BuilderI'm confused. Do you have the graph open in JMP? I created a small dataset to mimic your table. This is your graph builder graph (which I made by dragging three variables -- not a lengthy process). You then need to drag the column containing the Before and After information (my column is named Before/After) from the bottom of the graph to the Group X area, as indicated.
This results in this picture (only one drag):

Not a very lengthy process. What am I missing?
Graph BuilderHow to insert a dividing line between Before and After (see fig.). Figure done in Graph Builder (JMP 14)

Re: Graph BuilderMaybe you are looking for an old-fashioned reference line?
https://www.jmp.com/support/help/14-2/customize-axes-and-axis-labels-in-the-axis-setti.shtml#781878