How do you go about answering a "How Would The Audience Feel" question?

That's a little tough to answer since your subjective experience of the play will change the way how you think the audience would feel. However, I'll give you my opinion based on my own take on the play, and hopefully that will give you some inspiration to write your own answer. For my part, I would answer a "How Would the Audience Feel" question by saying that the audience would probably feel conflicted emotions in regards to the happy conclusion of Bassanio and Antonio's plot and the sad conclusion of Shylock's plot. 
Antonio and Bassanio are undeniably supposed to be the main characters in the play, as most of the main action revolves around their storylines. As such, we naturally want to see their stories end happily. However, though Antonio and Bassanio get what they want by the end of the play, their happy ending comes at the expense of Shylock the Jewish moneylender. Now, Shylock is usually seen as the villain of the play, as he basically wants to murder Antonio. However, Shylock also becomes a sympathetic character, as his anger is a result of the way his Christian neighbors, including Bassanio and Antonio, mistreat him. Thus, when Shylock is stripped of his dignity in court and essentially humiliated, it's hard to avoid empathizing with him. In that case, though the audience would probably feel a sense of happiness for Antonio and Bassanio, most members of the audience would also probably feel sorry for Shylock. This conflicted emotion that the play evokes is one of the many reasons the play has endured such lasting attention, both from scholars and audiences.