When Lennie first kisses Joe, she flashes back to a time when she was younger. She was lying on the ground, telling Uncle Big she was looking at the sky, and then Uncle Big said that the idea of the sky being above our heads is a misconception, and that the sky actually starts at our feet. Whenever Lennie spends time with Joe, she refers to the feeling of being in the sky.
Often, you can think of titles as a clue from the author about what the story, deep down at its heart, is about. This isn't always true (pro tip: nothing is), but there's a good chance it will be. The Sky is Everywhere is very much about dealing with death, yet the title refers to the sky, a.k.a. Lennie's feelings for Joe, a.k.a. love (more on this over in the "Symbols" section). Hmmm… it's almost as if Nelson is saying that love is the answer to healing after the death of someone close.
Or maybe Nelson is simply saying that love is everywhere and can be found even around something as sad as death. We don't think this one's super set in stone, so over to you now, Shmoopers.