I was skimming through Dungeon World today, and one of the GM Principles stuck with me: "ask [the PCs] questions and use the answers." Combined with one of the three bullet points on the GM's Agenda, "Play to find out what happens," a GM can make Knowledge checks a lot more interesting and engaging by soliciting player involvement.
What this means is that when a PC asks to roll a Knowledge check and you don't already have something in mind, if they succeed you can ask them to tell you what their character knows about the subject. If it ends up taking things in a completely different direction than you'd planned, well that's a great embodiment of "play to find out what happens." As an "explorer" type player, I like to learn details about the fictional world even when I'm GMing, and (for me at least) these types of twists make GMing a lot more enjoyable.
All of the sudden players might be scrambling to pick up some Knowledge skills for the chance to influence the narrative. There's a real, tangible benefit from the character's knowledge instead of some half-formed "fact" that often ends up being fairly pointless, if not entirely uninteresting, when the GM is forced to come up with something on the spot. Obviously this could potentially be abusable by certain types of players, and the GM should counter that without devaluing the skill by building off of the player's suggestion to keep it in-line power-wise, and/or varying the difficulty based on the specificity of the information. And ultimately, a roll should only be made where it's dramatically appropriate; players should know that they can't just knowledge-spam in an attempt to power-game (most players probably wouldn't go for that anyways).
Here are a few examples:
- The party finds an ancient religious text in some old ruins. Instead of the GM answering a successful Knowledge check with "it's a history of X deity," they ask the player "it refers to X deity, what interesting fact or legend have you heard regarding them?" If the fact is relevant to the current adventure in some way, all the better!
- When encountering a new type of creature a PC rolls a knowledge check to learn about any possible weaknesses. With a success, the GM says "ok, you can tell me a little-known weakness of this creature." This should be kept narratively interesting; answers like "uhhhh, it's vulnerable to swords because I'm carrying a sword" are pretty lame. As a GM, you can build on that by saying "oh yes, there are tales from ancient Akaras that say the beast is vulnerable to swords. Of course, all swords from that time were made from Akaran steel, so they felt no need to specify that an 'Akaran blade' was the beast's true weakness." Instant story hook, and now when the PCs seek out an Akaran blade they'll have a tangible mechanical advantage against this creature.
You can take this idea even further by employing a variant of the "fail forward" philosophy. That is to say, failure is not simply a dead end, but leads to a different approach that needs to be taken or a pseudo-success but with complications. Say a PC fails their Knowledge check (or in a system like Edge of the Empire, perhaps they even succeeded with Threat or Despair). You can provide one fact, and then ask the player to provide an additional fact. Alternatively, you can have another player at the table provide one of the facts. Then you roll randomly to determine which of those facts is true, and which is false. The player will know that one of the facts is false (just not which one), but the character will probably think that both are true. Acting on misinformation can provide interesting (and sometimes hilarious) results, but the player can't complain too much since they got something true out of the deal, too.
Alternatively, the complication might be that the player provides just one fact and the GM rolls randomly to determine whether it's true or false. This works especially well if nobody at the table can think of a second fact right away, and you want to keep the game moving at a fast pace. It's worth noting that the "is it true?" technique shouldn't be used for all failed Knowledge checks, because it has the potential to become frustrating. You definitely don't want PCs to be afraid to attempt Knowledge checks! What's "too much" will vary group to group, but once every few sessions might be a good baseline to start at.
When the GM rolls randomly any die roll that offers a 50/50 result should do just fine, but in some games it might be interesting to make a special type of roll. The Force Die in Edge of the Empire springs to mind (the GM notes one of the facts, and if a dark side result is rolled it's false, with perhaps more severe consequences if it's a double dark side pip). The "degrees of truth" idea can also be used with the feat die in The One Ring, making the d12 roll potentially more interesting than a 50/50 roll using a d6 (if the Eye of Sauron or Gandalf rune are rolled, up the stakes).