I would suggest using what the manufacture suggests. You could also check with a local dealership and use their recommendation. Just make sure that you use a motorcycle type oil as they are formulated specifically for the needs a motorcycle requires: clutch plates, heat transfer, valve trains , etc... ( more than likely will be a 10W/40 )
Use the appropriate Kawasaki motor oil per the manufacturer, usually 10W 40 or 20W 50. Each manufacturer has their own brand of oil specifically formulated for their engines, tansmissions and clutches. Check the owners manual and it will tell you exactly which viscosity is required for the model described.