I just don't know how to get my husband to talk to me. What can I do to get him to open up to me?
Without knowing your situation it's hard to know why he's not talking, so I'll throw out a few possibilities. Just to be clear I'm not trying to accuse you of anything, just putting out a few reasons why he might not be talking a whole lot.
Do you listen to him? If whenever he talks he feels (rightly or wrongly) that you aren't listening the chances are he'll consider talking to you to be a waste of his breath and save it. If you ask his advice on stuff and then appear to ignore it, don't be surprised if he doesn't have much to say next time you ask for advice.
Does he feel that what he has to say is interesting? A lot of the time life can seem pretty dull, and if he does a job that you don't understand he may feel there's no point in telling you about his day because you wouldn't understand anyway. I worked in IT for over a decade and rapidly learned there was no point telling my wife about my day in any detail because it went straight over her head. By contrast she works with disabled people and I've met several of them so when she tells me how Bill said this or Julie did that I've got some kind of connection to it.
What sort of talking are you expecting from him? From a man's perspective it often seems like women talk just to see how many words they can use up whereas men tend to talk to accomplish something specific. Where women use talking as a form of social bonding men are often less verbal. A bunch of guys can get a sense of social bonding by sitting around a fire drinking beer even if they aren't saying much, whereas I suspect a bunch of women sitting around drinking beer and not saying much would leave everyone wondering why nobody wanted to talk to them.
Related to the above, when problems are discussed men tend to talk around the problem with a view to solving it whereas women often talk about a problem with a view to just sharing. If a woman talks about a problem expecting a bit of empathy and support while the man approaches the discussion looking to solve the problem the conversation runs at cross purposes until one side (typically the man, being the less conversational of the two) gives up because he's being presented with a problem by someone who doesn't want a solution. From his perspective it's like taking a car to a mechanic, telling them how it doesn't run very smoothly, but not wanting them to actually fix the car.
Did something specific happen that caused a change? If he used to be quite chatty but now isn't, when did things change? I'm assuming if it were a major life event (death of parents, redundancy etc) you'd know about it and have considered it. But if it's something you don't necessarily know about perhaps trying to gently talk about situations to see if there is something there you should know about. That leads on to...
Does he know you're by his side come what may? It might sound obvious but if he's of the opinion that his job is to provide for you, to protect you, and to make problems go away for you, then if he's in a place where that role is threatened he might feel inadequate, like he's failed you in some way. For example, if he's facing a high chance of being laid off in the future and you're still earning a good income then he could potentially see it as you doing your job as the wife while also doing his job as the husband, and him therefore adding no value to the relationship. If that's the case then he needs to know that you love him for who he is rather than for what he does for you.