meaning of the phrase "issue of quantum of"
Solution 1:
I believe in this case your confusion is probably due to the word quantum. One of the OED's definitions for quantum is as follows:
Total amount or quantity; … in later use chiefly law (with reference to amounts of money)
So here, quantum is being used in legal settings to discuss the amount of money (damages) or the length of the sentence. Issue simply refers to an important topic here. The first example you provided is simply positing that the proper scale of costs should be determined on the basis of whatever damages the court decides upon.