Our support site is indexed pretty well by google; if I search for jsl for loop example I find Iterate at the top of the list. You'll probably land on a JMP 12 page rather than JMP 11, but most JSL does not change between JMP versions.
I absolutely agree with Ron and Craig above. Another good resource that is easy to get at is the Scripting Guide. From the Help Menu, click Books, then Select the scripting guide. The other really helpful resource is the Scripting Index which is also under the Help menu tab.
This Mastering JMP topic is pretty good too (I might be biased) except that I hear the presenter goes a little fast.