Everyday of my professional career and often outside of my office, I am confronted with this question. It's a powerful one. How do I get my child to open up? Before I teach you a powerful skill to do this, I want to spend a couple lines saying what doesn't work.
First off, asking them a yes or no question like "What's wrong?" or "Is something wrong?" or "Are you having a bad day," doesn't really work for kids who don't open up quite naturally. They will see the easy way out...and simply state "no" (emphasis on the no sounding like a noise and not a word, with head down at their phone and zero change in body language). The principled reason in not asking these simple questions is this...how often as an adult do you get confused about what's actually wrong with you? How often, when you are asked or you ask yourself why you're in a funk, do you actually struggle to know the answer? It's likely very often. We struggle at times to be able to see into our own world and break down the source of confusion...let alone then turn around and picturesquely describe it with emotional adjectives that poetry would be jealous of. But we want our teen to do that??? It ain't gonna happen.
The other reason the above questions are not great is due to the underlying message in them. I call this "the message in the message." In other words, when asking them about what's wrong, or are you having a bad day, there can be (emphasis on can) a quick reaction or defensiveness due to feeling judged, misunderstood, or being "zoo animaled"(being watched like an animal at the zoo).
Empathy is and always will be a win-win.
So here's something you can do instead. It's called emotional empathy. Emotional empathy is the act of putting yourself in your child's shoes and allowing your own human nature to teach you about what he or she has been going through or is feeling. This takes some preparation and I've found most parents miss the preparation step to really figure this out. In other words, taking a few minutes by yourself, even taking some notes, but really thinking to yourself, "Okay, my son has been really struggling with his friends, some of them don't care in slightest if he's around, his older sister is excelling in life quite easily, and he struggles at some of the basics in school. He hasn't spent quality time with his dad in a while, and I've been after him everyday to finish his basic duties." Sound familiar?! Taking this into account, if you were your son, what would you be feeling?
The first answer most and all parents and people usually forget to think is anger. I don't know why this is, because anger is an absolute primal emotion that comes very easily, yet we forget to normalize it. Other emotions I see in this kid are frustration, loneliness, inferiority, rejection, inadequacy, feeling stupid (powerful emotion for a teenage boy), controlled, not good enough, and possibly hopeless.
So here's the skill. Having prepared yourself, you very kindly and comfortably approach your son and start showing empathy, "Hey bud, I need to talk to for a few minutes and I need your full attention. Can you speak now or do you need a couple minutes? (he says yes lets talk). You look him in the eyes and say, I've been thinking about your life and some of the difficult things you've been going through. I know I've been on your case a lot and you haven't spent time with dad a whole lot...I also know that school hasn't come as easy to you as your sister, and that your friends have been kinda up and down with you at times. As I watch you, you don't show much emotion, but it scares me to think about what you're enduring alone. I know if I were in your shoes I'd be feeling pretty angry and downright frustrated, as well though, I think I'd feel kinda controlled, lonely, rejected, even stupid or inferior...you know...(look at his eyes, if he's staring at you intently it's because you're likely spot on), But I also know at your age, I don't think I could've really understood what those emotions really were. Am I just completely off base with what I'm saying, or are there things you relate with? What do you think relates to you?"
These are the principles I just used: 1. Permission 2. Empathy 3. Watch for reaction 4. Question of Relation 5. Listen, Listen, Listen
You will find as you try this that you are completely wrong at times. Your teen will say they don't relate. However, remember the message in the message principle. The message underlying the attempt at empathy is....I love you and want to hear you. Empathy is and always will be a win-win.