Still pretty new, and haven't had to check my reed valves, but as I understand it, One way to check them is to hold an index card or similar in front of your carb.
If the card or paper or whatever you use, blows away from the carb, then the reed valves aren't closing properly.. Carbs should only suck air/fuel in really..
The reed valves are behind the carbs in the intake manifold. They are supposed to open to let the air/fuel mix into the crankcase when piston move upward to top of it's stroke (creating vacuum in the crankcase), then they close so it doesn't come back out the carb when piston is moving down (creating pressure In the crankcase)..
There's no valves in the cylinder top like a car (or any 4 stroke).. 2 stroke has holes in the cylinder walls towards the middle/bottom.. One set to let fuel/air into the combustion chamber and another set to let exhaust out..
When the piston moves up past these sets of holes, they're blocked off from the combustion chamber, which is why the reed valves have nothing to do with your compression readings..
Again, Still pretty new, so it's possible I have something not quite right in the above statement, but that's how I understand it to work at this time anyway..
For whatever that may be worth... lol
