CHICAGO — Student editors at the newspaper covering Northwestern University have faced two waves of criticism over their coverage of protests in response to an event featuring former Attorney General Jeff Sessions. First, student activists criticized them for publishing photos of protesters on the suburban Chicago campus. Within days, editors at The Daily Northwestern decided to apologize, but their editorial prompted a second round of criticism from journalists around the country who said they shouldn’t feel any guilt about using basic reporting strategies. In the editorial, posted online Sunday and printed Monday, editors said they shouldn’t have tweeted photos of student protesters being blocked by campus police as they tried to get inside the Sessions event last week. The photos were later deleted.