Good question. I can't find a way to do this from the graph. That might be a good suggestion for the JMP Wish List.
I did find that if you go to File > Preferences > Fonts and change the font for "Text" that will change the font of group X:
![Phil_Kay_0-1634215593874.png Phil_Kay_0-1634215593874.png](https://community.jmp.com/t5/image/serverpage/image-id/36563i28575103B2584E3D/image-size/large?v=v2&px=999)
However, that will also change the font of lots of other text in JMP.
You could change the font after export from JMP. Have a look at the section "An added benefit of vector graphics: Infinite customization" in this JMPer Cable post.
I hope this helps,
Phil