Graph Builder doesn't export the internal data, but there are other mechanisms for getting the data from JMP. For instance, Tabulate or Tables > Summary will provide summary statistics. For smoother, an equivalent Fit Spline in Bivariate has a command to Save Predicted Values.
The main reason why I was interested in getting at the plotted data was because when I added a spline fit to my graph (multiple overlaid time series trends expressed as mean+/-SEM), adding a spline smoother changed the autoscaled y-axis values (it zoomed out to the point where I couldn't see my trends). So I thought maybe if I had access to the plotted means and SEMs, I could scale the axis manually by reading the max values of the arrays. I suppose I could use the Summarize function to get summary statistics and and Spline Eval function to get predicted values of the plotted data but it seemed like it might be more efficient to use the gb calculated and plotted data (also the summarize function does not seem to have the SEM statistic which I will have to calculate from SD and sqrt(count)).