What is it you want to know?
The 'Reverb" effect row is a system effect. That means exactly the same effect type and parameter settings applies to all 28 parts. For each part, you can select the amount that you want to keep 'dry' and the amount you want to put through the effect.
In addition to the system effects (reverb, chorus) each part can get its own dedicated effect which is know as an 'insertion' effect. Different models differ on the number of insertion effects available at once - Genos offers 28 at once (one on each part) while smaller models like PSR S950 allow only 4 at once.
Sometimes - and not too often, I would have thought - you want to use a different reverb effect type on a part. To do that, you would set the system reverb level to zero then select a different reverb effect as the insertion effect just for that part. Then you can set up its parameters however you want.