Hi Ruhail,
even i had the same confusion like you but i did not notice it 1st then i realized it after a while.
using the same report RPDLGA20,
in the selection screen ender the flowing as it is
country grouping
Wage type - (leave it blank if you want for all the wagetype)
Validity of wage type - (just give the end date if you want or leave that blank as well)
output (you can select any thing)
execute
now you can see all the Processing, Cumulation & Evaluation classes, which are assigned for each of them (i mean e.g what are all the wagetypes that are assigned to a particular cumulation class)
Regards
Rahul