To give yourself, or another player a Shulker Box, use
/give <Player> shulker_box
You may also use give yourself, or another player a
colored Shulker box by using the same command:
/give <Player> shulker_box:<color code> up to color code 16!
Shulker Boxes can be crafted by using
Shulker Shells which can be obtained by using
/give <Player> shulker_shell