I use all of Show Property(obj), Scripting Index, Scripting Guide and JSL Syntax reference (Scripting Index is definitely the most important one for me). For JSL Syntax reference I tend to utilize the .pdf as I consider JMP Help pages search to be so horrible that it cannot be used https://www.jmp.com/en_fi/support/jmp-documentation.html (you can also get Scripting Guide and other documentation as .pdf). Or first I use Scripting Index and then click topic help as this helps (hopefully) to navigate to correct page on JMP Help.
Be careful though, different documentation do not necessarily agree... JMP Scripting Index feedback and discussion this is a bit old topic now and some of my understanding has improved since regarding the syntax but if I remember correctly it does contain some examples of discrepancies between different documents.
-Jarmo