Find any of the 3 largest among $n$ elements
I don't know what do you mean by comparison graph. However, here is my solution for question 1. 

Suppose you have a list of $m$ elements, and you want to find the largest element. You can do this with $m-1$ comparisons.

Do you know how to proceed?


    You can simply ignore the first two elements in your list. This gives you a new list $L'$ of $n'=n-2$ elements, You can determine the largest element of $L'$ with $n'-1=n-3$ comparisons. This element is one of the three largest.