The latest Chinese 110cc's I've seen (and owned) will spec 15w40 right on the chassis name-plate. Obviously a HD/aircooled or motorcycle 10w40 would be good too. They run hot because they're only cooled when your in motion. There's no oil filter on them. Also be sure to not accidentally add oil to the plug on the stator cavity. You wouldn't believe how many have done that. The oil fill has the dipstick.
Be careful with the oil drain plug. Don't remove the bottom plug that sets at an angle. That plug is for the timing chain tensioner. Not a big deal if you pull it, just put the parts back in, in the order they came out (spring and shim, etc). The drain plug is the one facing straight down.
Joel