Your question has several possible answers because Nick Carraway attends a number of 'events'. The most prominent  event he attends is Gatsby's party. After watching the nightly events at Gatsby's mansion from his front porch,  Nick receives his own invitation to attend one of Gatsby's parties. Nick is seemingly more curious than flattered, but accepts for both accounts. In addition to Gatsby's parties Nick Carraway attends a dinner party with Daisy and Tom, and he travels to New York with Tom and Myrtle attending a party at the apartment Tom keeps for her. Lastly, besides Gatsby's father Nick Carraway is the only person who attends Gatsby's funeral. The great irony lies in the stark difference between the lavish parties with all of Gatsby's so called 'friends' and the absence of those 'friends' at his funeral. The only friend to attend that event is Nick Carraway.