"easiest of questions" = the easiest question imaginable, very possibly referring to just one question.
"Will you marry me?" "That's the easiest of questions: of course!"
Other examples: "He was the bravest of men", "Those were the darkest of days", etc. It's a formulation that lends itself well to high-flown or ceremonial writing, but isn't exclusive to it, though I'd say it's much more common in written than spoken English.
"easiest questions" = the easiest questions from a defined group of questions --
The teacher could've quizzed me on anything, but for whatever reason, she asked the easiest questions.
-- or a common form of hyperbole that often omits the second half of the statement, where the speaker would normally specify what the superlative (-est) is being compared to:
That was the easiest test (I've ever taken).
I was asked the easiest questions (I've ever been asked).
He was the nicest guy (I've ever met).
I personally find the first sentence more natural, but it depends on the intended meaning.