Does this card just not… work? If I recall correctly “IF this skill test is successful” resolves in step 7, while “AFTER” in step 6. It so happens to be that most effects that depend on how much you succeed by trigger before Inquisitive has a chance to have any effect: Lucky Cigarette Case, Antikythera, Precious Memento, Alton O'Connell, "I'll take that!"…
Fertigkeit
Innate.
XP: 1.
Assistant, Miskatonic, Scholar deck only.
If this skill test is successful, the performing investigator may succeed by up to 2 more or down to 2 less (to a minimum of zero).

FAQs
No faqs yet for this card.
Reviews
Even if this card worked the way that the designers clearly wanted it to, it seems overly specific. There's only one archetype that cares about succeeding by specific numbers - Exact Number Seeker. Oversuccess Rogues might have this competing acting as three boosts, and they'll usually have Savant filling that role if they aren't already pumping the number in other ways. For everybody else, good old Unexpected Courage exists and works better for their cases.
So, this is only useful in a specific archetype (and lucky for that archetype, most of the time the deck building restriction is going to match). Is it going to get a lot of mileage? That's somewhat limited. Innate isn't a particularly useful keyword - it combos with True Survivor, which could be helpful for Darrell Simmons, but that's pretty much it. (Darrel and Alton O'Connell could make for an amusing duo, though.) It also only boosts a single use, meaning it's not going to go as far or be as flexible as tools like Artistic Inspiration, which can act as mini-Lucky! on demand, or Steady-Handed, which can incidentally heal horror as well. And out of the cards that care about exact numbers, the more impactful ones (Chemistry Set or Antikythera) already have successful results within a range of two numbers - which means you really don't need to tune that much. Sure, this could help enable Alton O'Connell or Dr. Charles West III - but spending XP just to enable them once seems like a stretch to me.
This isn't bad, but it's fairly low down the list of exact skill enablers - there are better options before then. And once you have those in play, I don't think you need this. Unless you're really eager to see Carson Sinclair use a Katana, this falls a step behind for its XP cost.