You know that Juliet is not dead even while the Capulets plan funeral What literary device being employed here?

Dramatic irony occurs when the audience or reader is aware of something that a character in the story is not.

In this case, the audience knows that Juliet is not actually dead, but the Capulets are planning her funeral, unaware of the truth. This creates tension and suspense, as the audience waits to see how the situation will resolve itself.