Expose Evil

• WOTC Official Reminder Textofficial rules
  Investigate — Create a Clue token. It's an artifact with ", Sacrifice this artifact: Draw a card."

• WWizards of the Coast2016-04-08
  Official Ruling
  If an effect refers to a Clue, it means any Clue artifact, not just a Clue artifact token. For example, you can sacrifice Wrench to pay for Alquist Proft, Master Sleuth's activated ability.
• WWizards of the Coast2016-04-08
  Official Ruling
  You can cast Expose Evil with no targets if you only want to investigate.
• WWizards of the Coast2016-04-08
  Official Ruling
  If Expose Evil has at least one target and all of those targets become illegal, the spell doesn't resolve and you won't investigate.
• WWizards of the Coast2016-04-08
  Official Ruling
  You can't sacrifice a Clue to pay multiple costs. For example, you can't sacrifice a Clue token to activate its own ability and also to activate Alquist Proft, Master Sleuth's ability.
• WWizards of the Coast2016-04-08
  Official Ruling
  Clue is an artifact type. Even though it appears on some cards with other permanent types, it's never a creature type, a land type, or anything but an artifact type.

Rulings via Scryfall