These are all the commands in the game, from common commands to the Easter egg/secret voice commands. If I have missed any let me know, I will add it if I can verify it.

These are all commands you can say in game to get interactions from the ghost.

• Where are you?, Are you here? (Works best on Ouija board giving you precise location.)
• How old are you? (Works best on Ouija board)
  
• Goodbye. (Ouija board, Keeps ghost from drain sanity.)
  
• Can you talk?, Are you friendly? (Works best on Spirit box.)
  
• Do you respond?, Are you shy? (Works best on Spirit box.)
  
• What is your name? (Works on both.)
  
• When did you die? (Works on both.)
  
• Are you here?, Are you close? (Works on both.)
  
• Blow out the candle. (Candle command)
  
• Swearing: F**k, F**ker, B**ch, And Mother F**ker (Makes specific ghost angry.)
  
• Give us a sign. (General command)

These are all commands for the secrets and Easter eggs.

• Piano.
  
• See you.
  
• Beer.
  
• Volcano.
  
• Call me.
  
• Lust.
  
• Smile.
• Victoria.
  
• Banshee.
  
• Crazy.
  
• Romero.
  
• Bloody Mary (x3)
  
• Anger.
  
• Limbo.
  
• Ball.
  
• Magna.
  
• Dream.
  
• Nightmare.
  
• I want to join the cult.

I will not include locations for the Secret/Easter Egg locations, as you should find these one your own.

Good luck hunting, and remember a crucifix in the pocket will save your life.

Here is a compiled list of other guides from various creators that may answer more questions pertaining to game play or Easter eggs.

• Demonologist | Complete Guide
  By SubmssvHellkitten
  
• How to use the Tools to Gain Evidence
  By Tom
  
• Ghost Types and Evidence
  By Wendy
  
• Demonologist 100% Achievement Guide
  By Raptvre