There should be a VIN number on the frame, often across the front tubes behind the nudge bar. This doesn't always have a maker code on Chinese bikes, but does have the date and country of origin. There will also be a number on the engine, this often has the type of engine as well, i.e, the GY6 series has GY6 as part of the engine number although several different makers manufactured them.
The GY6 ATVs I have messed with have a "QM" # as part of the VIN. e.g.
a "157QM" unit will have a 150cc engine. Knowing it is a GY6 motor is
often good enough to find engine parts, but not good enough for peripherals:
brakes, electrical, suspension, etc.
HiSun puts its maker mark often on the top of the cylinder head. CFMoto
often puts its marks inside the motor, unfortunately. These are 2
really big companies.
Parts are cheap, but you often need to buy them based on the photo and