What else shall I do here?

Hint 1 of 4:

Write a message of your own.

Hint 2 of 4:

You want to find out where the voodoo conclave is held.

Hint 3 of 4:

Have Dr. John bring something that you will be able to follow.

Hint 4 of 4:

Have Dr. John bring the small ritual coffin from the museum.