So I actually built a JSL plugin for notepad++. I'll say how to install it below, but might I recommend the JSL for VSCode extension that we moved to instead. It's under (semi-)active development and has much more extensibility. You can find it by downloading VSCode and searching extensions for "JMP" or in the VSCode marketplace.
But if you just really like notepad++. Here's how to install it.
Find your install directory, by default it’s C:\Program Files (x86)\Notepad++
Go to .\plugins\APIs
Drop jsl.xml in there
If you have cloud settings setup in in N++, go there if not go back to the install directory
Open your functionList.xml
Open funcitonList(JSL).xml from the zip
paste its contents in as another parser below </associationMap>
Save and close
Open your userDefineLang.xml
Open userDefineLang.xml from the zip and paste that in as another lang wherever looks appropriate