Does an oil with an API Rating of SN (the most current) meet the standards of all proceeding ratings (SL/SJ in particular). The generator specifies "SL/SJ" but I'm having trouble finding it. Can I use "SN"?
You are fine to use the API SN rated oils. Here is an excerpt from the API website:
Introduced in October 2010 for 2011 and older vehicles, designed to provide improved high temperature deposit protection for pistons, more stringent sludge control, and seal compatibility. API SN with Resource Conserving matches ILSAC GF-5 by combining API SN performance with improved fuel economy, turbocharger protection, emission control system compatibility, and protection of engines operating on ethanol-containing fuels up to E85.