I presume it should be a standard 3/4-16 threaded filter used on most small engines, look for the filter that fits most newer Fords, the equivalent to Fram's 3614 or Motorcraft's FL910
I use a Motorcraft FL910S. It seems to be a very god filter at a very good price from Walmart. The FL400S is a PITA to get in and out because of the extra length, so it makes a mess on my 15hp Kohler.
On the two riding mowers I owned with Kohler V-twins, there was plenty of room around the oil filters so I ran FL400 equivalent filters. One was a 20hp Command, the other was a 20hp Courage.
I've had a standby generator for 15 years. Why would you want to overpay for an oil filter like a Mobil 1 filter for a generator that requires oil changes every 50-60 hours of runtime?