If you're having trouble coming up with answers, maybe you need better questions.
Discern Realities, as the game procedure, is about asking some subset of those six generic questions and receiving answers to them, usually with a +1 forward attached. However, that's only half the move.
Discern Realities, as the story of your game, is about the PCs formulating questions that reflect some subset of those six generic questions, and the actions they take in order to find out the answers.
When your players make the Discern Realities move, they should be able to ask one question from the Discern Realities list, as it maps to their current situation, and tell you how they're planning to get the answer.
As a GM, you have to tell the truth, but the true answers you give to the Discern Realities questions should reflect the scale and methods of the investigation. When Leafwillow is talking to scouts and leafing through old reports and doing some squirrel recon to try and plot a safe route for the caravan through Crashing Boar territory, that can all be wrapped up in one Discern Realities roll if you have a mind, and the questions she gets will be answered by her and others' observations in ways that apply to the whole Crashing Boar situation. These answers can tend to be more of the big sweeping backgrounder kind because you're responding to a big sweeping question.
When it's day 5 on the road and a Crashing Boar comes crashing out of the undergrowth, pulls a sick bootlegger turn, and blows out the lead wagon's rear axle in a hypervelocity trail of hirsute porcine afterimages, that's a much more specific situation. And when Leafwillow stomps her wooden leg on Fightgar's cloak as he's about to heft Endbringer and leap off the caravan screaming for blood, pleading that "we must try and understand this creature", what follows is going to be a very different set of investigative tools, which demand their own answers from Discern Realities. These are much more likely to be short, punchy answers that only relate to the current combat, because combat, like Fightgar, is short and punchy.
One easy thing you can do as a GM to set up giving appropriate answers is asking your players how the fictional actions they're taking are going to provide those answers. This isn't some chapter-and-verse gotcha, you just need to know how the story goes.
Steve, player of Fightgar, doesn't know diddly about reading wild animals, but Fightgar's an old hand on the caravan trail and has plenty of experience dealing with animal attacks. Fightgar wants to protect the caravan so he's watching the boar spin out and brace itself - is it running to something? From something? What's about to happen? (Or maybe, what should he, Fightgar, be on the lookout for?)
Of course Fightgar can Discern Realities in combat. Fightgar may have taken the advanced move Seeing Red, which gives him +1 to Discern Realities in combat! (Actually, that means pretty much anybody can Discern Realities in combat. It'd be pretty weird to get a bonus to something impossible.) But, crucially for your situation, all Fightgar's doing is making combat observations and trusting his combat instincts to come up with combat answers, and you should already have those answers.
Portray a fantastic world. Embrace the fantastic. Name every person, give every monster life. What those principles mean is that when, as GM, you set a scene and put somebody in it, you take on the responsibility for defining that scene and setting that character's motivation*. And when the scene is combat, the characters are all the combat participants. When the caravan is attacked on Day 5 by a Crashing Boar, that's not just a random result from some behind-the-GM-screen table that you've been saddled with. That's your battlefield and your boar, to define and use how you see fit. Answering Fightgar's Discern Realities questions is a chance to share your decisions.
What is about to happen? What should I be on the lookout for? These are a chance to share your thoughts about motivations and other details of the monsters you've put in the scene. Judging by what the boar is keeping an eye on as it spins out, it's aiming for a head-on collision with the central caravan wagon.
What happened here recently? What here is useful or valuable to me? These are a chance to share your thoughts on the battlefield as it interacts with your monsters and their motivation. Like maybe, the track the Crashing Boar cut along the caravan trail isn't new. You can see patterns of old and new undergrowth and it's following them like a slot car on a track.
Who's really in control here? What here is not what it appears to be? This is your chance to start teasing at the iceberg underneath the current combat setup. Like a different maybe, this spinout isn't all the Crashing Boar's doing. It wants to go in one direction but something is goading it, aiming it at the caravan instead.
And hey, that's three categories of questions, more than enough to answer any Discern Realities that rolls. Neat, huh? Why isn't Fightgar rolling Discern Realities in combat all the time?
*I'm talking "character" as in "would be a credited role in a movie"** - when you set a scene in a bustling town market it's hardly reasonable to expect you to outline anything about the motivations of the "background extras" like customer number 18 at the dried fish stall.
**The Crashing Boar, of course, is yet another credit for the vocal stylings of Frank Welker.
Using The Answers, Or, Why Fightgar Isn't Rolling Discern Realities In Combat All The Time
Let's get the simple counter to "all the time" out of the way first. Fightgar can't just keep rolling Discern Realities in the same combat because combat tends not to present different realities as it goes on, to Fightgar or Fightgar's friends. One bite at the apple is all anybody gets, unless something about the reality of the combat changes - like, say, this was that control scenario, and Clericsdottir exorcises the spirit that was driving the Crashing Boar and opens up a second front. You already know how much Fightgar can discern about the realities of combat - rolling twice doesn't somehow get you more information.
But even that first bite at the apple is a risky bite to take! Combat is a chaotic state of affairs that will imminently pitch danger to anyone at any time. (This is, of course, distinct from the dungeon, which is a chaotic state of affairs that merely can imminently pitch danger to anyone at any time.) However, there isn't anything like an "initiative pass" or a "player turn" in Dungeon World. People take the lead in the conversation for as long as it makes sense for them to have it, and in a high-stakes situation that usually means long enough to do one important thing before the spotlight's focus shifts elsewhere.
Always lean forward with the danger of the combat state, so people have something appropriate to react to. If taking the time to Discern Realities will get Fightgar smacked, then tell him the requirements or consequences and then ask. This isn't to say that Fightgar is a sitting duck while he Discerns Realities; this is a combat situation, of course he's got his guard up. It doesn't necessarily mean that Discern Realities is the only thing Fightgar does when he has the spotlight, either - if your Fightgar isn't a particularly tactical Fightgar, happy to take the measure of the battlefield and pass on advice to whoever needs it, then it's probably a bad idea to deny him the chance to follow up on his own leads when he decides not to let Endbringer do the talking for once. What it does mean is that Fightgar has focused on one thing about the combat, and even if there was no imminent danger to Fightgar, an easy go-to for the next person to get the spotlight is to talk about the dangers posed by the things Fightgar ignored. Or, heck, if Fightgar got multiple questions that revealed +1-forwardly true things about multiple vectors of badness, talk about what Fightgar isn't pursuing. Not in a "you idiot, Fightgar, this is what your choices have done to Shanksworth" sense, just -- it's combat. It's dangerous to everyone all the time. Here's the next dangerous thing. This has a couple of corrolaries:
Because combat is chaotic and dangerous, your scope for +1-forwardness of useful answers is a little wider. You still need motivations for everybody in your combat scene, and Discern Realities is going to be useful in exposing those. It's neat if there's also some battlefield secret or hidden agenda to play into, those are great variety, but if you didn't prep them as important things, don't feel pressured to invent some battlefield secret or hidden agenda to play into. In the chaos of combat, knowing that all is as it seems and you can put your all into the fight -- isn't that worth +1 forward?
Yes. Yes, it is, as long as you the GM say so. What, your players are going to rise up and revolt because they're getting the bonuses they rolled for?
Because the dungeon is also chaotic and dangerous, even if learning one more thing helps end the fight, it doesn't solve everything. I mean, maybe Leafwillow's right and understanding the Crashing Boar is really important. Maybe this is that slot-car scenario from above, and when Fightgar hustles to bend lift some gate bars and get the central caravan out of the Crashing Boar's way, it accelerates back into the deeper forest and doesn't look to be coming back. Okay. Now the caravan's sitting in the middle of the Crashing Boar expressway with a busted wagon and some panicking draft animals, a state of affairs not unadjacent to what would happen if Endbringer screamed for blood and Fightgar rolled max damage again. There's still the question of if the caravan can get underway before another Crashing Boar comes down the lane - and if it can dodge future intersections in the same way.
And this is assuming getting an answer from Discern Realities also gives you a clean way out of the fight! It could just be that this one of those famous scenarios where knowing is half the battle, and there's still the "doing" half of the battle ahead, which tends to involve red lasers and blue lasers for some reason.
And a final endnote, it really, really helps to actually note down what you answered for Discern Realities and if someone's cashed in that answer for +1 forward yet. The dry-erase notecards that aspect up my Fate games on the fly have also served excellently as floating Discern Realities bonuses when I run in-person Dungeon World. If you just run Dungeon World as a simple stream of text or voice, it helps enormously to also have some kind of shared prop space to track these things.