In the example sentence, "of sizable sums" is a subordinate phrase that describes the amount of money. "of money" is also a subordinate phrase describing "defrauded". Normally subordinate phrases give details about another part of a sentence but if removed from the sentence doesn't change the basic meaning of that sentence. I marked non-critical (to the basic sentence meaning) words in parentheses below. These parts of the sentence give details to the main sentence, but removing any or all of them will leave the basic sentence meaning intact.
A ((state owned) (cooperative)) society has been accused of having defrauded (scores of) (unsuspecting) students ((of sizeable sums) of money (as tuition fee)) (by enrolling them (in vocational training course)).
Removing some of the words and phrases marked above leaves us with:
A state owned society has been accused of having defrauded
scores of unsuspecting students by enrolling them.
Removing all of the marked words leaves us with:
A society has been accused of having defrauded students.
This last sentence has its basic meaning intact, despite removing 2/3 of the words.
When a sentence has subordinate phrases describing other subordinate phrases it makes that sentence very difficult to understand. It is also an indicator that the sentence should be probably re-written to make it easier for readers to understand. Learning to spot and ignore subordinate (non-critical) phrases and words to determine basic sentence meaning, as well as determining which parts of a sentence descriptive words are giving more details about are both important tools help determine meaning from overly complicated or badly written sentences.