Presumably:

https://openscad.org/cheatsheet/

Note that updating it is one of the blockers for a new release, so it doesn't include some newer features/syntax

There is also:

https://cubehero.com/2013/11/19/know-only-10-things-to-be-da...

FWIW, when I need to rough something out in OpenSCAD, I usually use:

https://www.blockscad3d.com/editor/