Question #1: The English verb for the negative of satisfy is dissatisfy. As far as I can tell, there is no reason discernible in the meanings of the prefixes un- and dis- why dissatisfy should have prevailed over unsatisfy—any more than why disarm prevailed over unarm as a verb—but it happened.
Question #2: The question asks which of the four options ("such a fit runner," "so fit," "so a fit runner," and "such fit runner") is NOT correct as a choice to fill in the blank in the sentence "He was ______, he could do 10 km and not even sweat!" The first two options work fine in that sentence, so the answer that the test giver deems the right one must be one of the other two. Unfortunately, as you have reproduced them from the test, both "so a fit runner," and "such fit runner" are faulty—and therefore either would be a valid answer as the INCORRECT choice. I suspect that you accidentally transposed "a" and "fit" in "so a fit runner" (since "so fit a runner" would be irreproachable English); that would leave "such fit runner" as the remaining INCORRECT choice, and therefore the right answer. The problem with "such fit runner" is that it omits the "a" before "fit runner," and in English including the indefinite article is standard in the singular form of such an expression (see?).
Question #3: Again the question asks which of the four options ("such fast", "such a quick one", "so quick," and"so fast") is NOT correct, this time as a choice to fill in the blank in the sentence "The train was _______________, it went from Tokyo to Osaka in two and a half hours!" The answer that the test giver wanted was "such fast." The other three options yield perfectly acceptable sentences when used to fill in the blank. So the issue here isn't some fine distinction between "quick" and "fast," but (once again) a problem with framing "such X" correctly.
It's easy to fall victim to test questions that break up a long series of questions asking "which of the following is correct?" by instead asking "Which of the following is not correct?" I suppose you could argue that such switcheroos enable the deviser of the test to (slyly) test how carefully the test taker reads instructions; but in view of the pressure that the test taker is under to complete the exam before time runs out, and considering how easy it is to miss the word not as you read what looks a lot like yet another iteration of the familiar instruction "Which of the following is correct," I think it's a cheap way to produce incorrect answers. (For evidence that the format is deceptive, you need only look at some of the comments and answers offered here to the OP's question, in which several well-informed English speakers likewise misread question 2, question 3, or both as asking "which is correct," instead of "which is not correct.")
I think it would be fairer if such test questions began with a sentence underscoring the against-the-grain nature of the negative question—something like "Three of the four multiple-choice options offered for this question are correct. Which option is not correct:"