"As If": This was added to the FAQ (v.1.7, March 2020) and then amended (v.1.8, October 2020). You can read the October ruling on the ArkhamDB rules page here. (I'm adding a hyperlink rather than retyping the rules in case in future the ruling is changed or amended - at that point, the rules page will be updated and all ArkhamDB FAQ entries will link to the correct ruling.)
Q: If I use Sixth Sense to search at a location in "City of the Elder Things" and draw a , and then use Sixth Sense's ability to search at a connecting Labyrinthine Chamber with a key on it; does the modifier of the token I drew get doubled? A: Yes. Assuming Labyrinthine Chamber is a connecting location with a “key” on it, and you have revealed a token using Sixth Sense, if you were to decide to instead investigate on the Labyrinthine Chamber, you would technically still be on Step 3 of “Skill Test Timing”, revealing a token; so yes, you would have to double the modifier based on Labyrinthine’s ability.
: Investigate. Investigate using instead of . If a , , , or symbol is revealed during this test, you may choose a revealed location connected to your location; you are now investigating as if you were at the chosen location instead of your location (you may use either shroud value).
Sixth Sense competes with tried-and-true Rite of Seeking. They are both level 0 Mystic Spell assets that let you investigate with willpower in place of intellect, which can be a crucial ability for low intellect investigators such as Agnes and Akachi. Let's compare these two Spells:
Sixth Sense picks up clues one at a time, whereas Rite of Seeking picks them up in twos. Rite of Seeking is therefore more action efficient at clearing multiple clue locations, which gives it an advantage in high player counts by accelerating your clue gathering. In theory Sixth Sense can create action efficiency by saving actions that would have been spent moving, but obviously saving the skill test on an extra investigate is usually better. When playing solo though, Sixth Sense is just as fast against 1 clue locations.
Sixth Sense costs 3 resources and Rite of Seeking costs 4. Not a major difference but it might be important if you are playing Dark Horse.
Sixth Sense doesn't deplete charges. With Sixth Sense in play, you can investigate using as often as you like.
Sixth Sense rewards you for drawing , , , and tokens where Rite of Seeking punishes you (or at least restricts its use to your last action). This might make Sixth Sense more desirable for Jim Culver who is already encouraged to increase his odds of drawing tokens.
The reward Sixth Sense offers you for drawing a funky token is worth talking about in more detail because there's a lot going on there. It will allow you to sometimes investigate at dangerous or high shroud locations that you might otherwise be locked out of. It can also protect you from token effects, large negative modifiers, and the Haunted keyword by lowering the shroud of a location you are investigating (although you must change the location you are investigating at in order to use this effect).
Unless you're willing to use Dark Prophecy this effect isn't reliable, but it is a kind of insurance against the chaos bag. Finally, a location must be revealed for Sixth Sense to let you investigate at it instead or use its shroud, meaning it pays to follow another player around, investigating to pick up clues left behind with the added possibility that you sometimes get a clue from a location they just revealed instead.
To conclude: Rite of Seeking is still the premier level 0 Spell for picking up lots of clues quickly, but Sixth Sense offers a persistent and highly reliable way to investigate using willpower. Having played a little with it at this point, its definitely a strong card for allowing Mystics to consistently contribute to investigating, so try it out!
Do all parts of that "as if" from the FAQ apply here?
Don't attacks of opportunity occur before you reveal the chaos token? ("An attack of opportunity is made immediately after all costs of initiating the action that provoked the attack have been paid, but before the application of that action's effect upon the game state.")
This card specifically says "You are now investigating as if you were at the chosen location", so surely the attacks of opportunity don't happen here?