This plugin isn't being updated anymore, and for it to work 100% you need my other plugin Genuis Core. But I just added this feature to the Genius Core plugin

Genius InventoryControl is plugin that helps staffs with checking player's inventories and ender chests

commands:

• /invsee [player] | Allows a player to view others inventories.
  • Aliases: /inventoryview, /inventory, /iv
• /enderchest [player] | Allows a player to view others Ender Chests.
  • Aliases: /ec, /echest

permissions:

• genius.inventory.use.others | Allow a player to view others inventories.
• genius.deny.others.view.inventory | Deny others from viewing their inventory.
• genius.enderchest.use.others | Allow a player to view others ender chests.
• genius.deny.others.view.enderchest | Deny others from viewing their ender chest.