“It is a sin to kill a mockingbird”. Connect this metaphor to a current event or event in recent world history.

In order to connect the quote to an event, you have to understand the quote first.  Atticus tells his children that they can shoot at tin cans and bluebirds, but that it's a sin to kill a mockingbird because, as the children learn from Miss Maudie, mockingbirds do but one thing: make music for us to enjoy.  It's then easy to label several characters as mockingbirds in the book, the most obvious being Tom Robinson.
In the case of Tom Robinson, you have a man who is clearly innocent and trying to do the right thing but is now facing death simply because of the color of his skin.  Trayvon Martin could be considered a modern-day black man who was killed due to racial prejudice. In this case, another man felt threatened simply because Trayvon was black and wearing a hoodie. Michael Brown in Ferguson, or Ezell Ford are cases that are also arguably questionable in that both boys were killed by police even though they were unarmed (Ezell also had a potential mental disability).  All of these deaths have resulted in protests against racial profiling or simple racism within our society and, especially, our police force.  Every one of these could be considered modern day "Mockingbirds."