Take off the cover plate on the bottom. You'll need a special torx socket to get the cover plate off. I suggest you replace the 2 cover plate screws with cap screws and dump the torx machine screws. See if the drain plug is tight. Check the oil level and make sure the O-ring is on the dipstick. Onan 4K gennys are known to mark their spot if overfull or the dipstick is loose. There are several gaskets on the head and elsewhere that can leak. Spray some brake clean on the engine and inside the genny cover to see if you can find where the oil is coming from. Not to worry just yet.
Chum lee