Anna Kepner should’ve been walking across the stage with her classmates this weekend ... instead, her grieving father accepted her diploma through tears as the crowd rose to its feet. Christopher Kepner attended Temple Christian School’s commencement ceremony in Titusville, Florida ... six months after Anna was killed aboard a Carnival cruise ship. Watch the video, obtained by "Good Morning America," that shows him wiping away tears as he walked onstage to collect Anna’s diploma following a