This is an issue that was covered in a previous discussion The following is the response from JMP about the bug:
"The issue with the Y axis is a known problem in JMP 13.0 and is expected to be corrected in JMP 13.1 when it is released during the first quarter of 2017. There are some cases where the axis will not be shown. The workaround for this is to make any change to the axis at which time the axis will be displayed.
There was a deliberate change in the X axis for nominal variables in JMP 13. The intent was to show as many labels on the axis as possible within the given space while still rendering them readable. The development team is considering different approaches for the issue. I am sorry for any inconvenience it may cause. "
(they gave me the OK to post and even reworded it a little more concisely ... another reason to love JMP support!)
I have found that simply dragging the graph from one monitor to the other of my dual screen setup will force the Y-axis values to display, as well as choosing 'copy graph' from the edit menu on the graph.