Actually, let's give
@Peg Marion a little credit and assume that we are a last resort after searching google, calling the retailer and/or manufacturer, asking around, and not finding anything.
A good question would have included these facts, because that's where most people would go first.
Having looked at the google hits, and having read what may be the
owner's manual, the information doesn't seem to be obviously available. The manual does tell you to check, clean, and set the gap on the spark plug. Possibly this item is expected to have a life similar to that of the rest of the generator and should not normally require replacement?
The fact that the same google search points to a
service kit containing oil, a spark plug and some filters points to the spark plug having a limited life, or (possibly at least somewhat correct) people being unwilling to do anything other than simply replacing spark plugs these days. This kit does not disclose the type of the spark plug.
The briefest of searching within the same page shows that you can also get a
"specially selected" spark plug for under $10. Given that they don't tell you what the spark plug is, I suspect the nature of this special selection is cost. However, presumably, buying just one o these would reveal the type of the spark plug (as might looking at the old one) and allow you to buy the same, or functionally equivalent one. Additionally, the fact that they sell these in anything up to 10 packs, and haven't received a single "rating", I would suspect that the spark plug is common to a lot of generators.