Welcome!
Firstly, when dogs are rehomed it can upset them and you will probably be handling him in a different way to his last owner etc which may be confusing him. Don't forget he's going through a lot right now and doesn't really know you or your family and taking commands from a total stranger is not something he's had to do before and if you are unfamiliar with owning a dog too then you're both learning a lot right now! He's clearly had a lot of work put into him and if you've got a one year old worker with good recall you're very lucky and you should be able to get everthing else sorted pretty quickly!
Your best bet would be to find a really good training school, explain the situation and get yourself signed up so you can learn how to work with him and how to think 'dog' and train him in a positive way and start building the sort of bond he had with his last owner. Try not to give him commands repeatedly, wait until you have his attention then give him a comand once. If he's not responding don't keep repeating it as you are only teaching him to ignore what you're saying. With 'sit' for example, try holding a little treat (something like a very small piece of ham) in one hand then give him the comand as you raise the treat close to but above his head, as his head follows it up he should sit anyway and as soon as he does praise him and reward him with the ham - you could be shown how to use a 'clicker' by a good trainer to make sure he knows when he's done what you were asking and that's why he was rewarded. you make it 'click' as soon as his bum touches the floor so he knows that's why he's got the treat.
There is lots of wonderful info on this site so do lots of reading on here, get yourself along to some good training classes (ADPT certified with positive training methods only) and you will really start to enjoy everything that comes with owning a working cocker - they can be hard work and need lots of mental stimulation and exercise but are so rewarding and SO much fun!
Let us know how you get on!
Hannah xxx
Learning to work 'with' your dog is so rewarding