For training your pup you need to be consistant. You need to take time everyday to work with him, at his age I would say at least 3 twenty minute sessions a day. The first command he needs to learn is focus. Some trainers call it look at me, I call it focus. Basically though pick a word or you can even use his name. What you will teach him is everytime you say it he is to make eye contact with you and wait for a command. Start by showing you have a treat but hold it low, when he focus on the treat say the word and raise it to your eyes when he makes eye contact praise and treat. As he gets better no treat just praise and eventually you should just have to say good as a reward(I say thank you and pup knows she did good). Your goal is to get him to focus on you as soon as you say the word and to not stop until you release him. Once he has focus down the rest come pretty easily
Next work on come. Some times a whistle helps with this because it can break distraction. The idea is when he has it down he could b mid chase(let's say squirell) and when you yell come he will stop dead in his tracks and run to you. Start with baby steps a few feet then farther then with distractions. If he has focus down he will catch on easily.
Next is sit,then stay, then lay, etc.
Never use the same word for different things so if you use down for not jumping or off the couch. Then use lay for lie down. Or use down to lie down and off for couch or jumping.
Always start with treats and ween your way to a praise word
For walks he needs to learn not to pull it is easier to teach him this if you work out some of his pent up energy first. Before walks take him in the back yard for 15-20minutes of fetch, then try a walk. Always make him sit to be leashed. Once leashed he should stay sitting until you say let's go. You need to walk at a slow calm pace. Until he knows how to walk he should not be given any extra lead and should not be out in front. Use a short leash 4 feet. When you start to walk have him at your side leash taunt when he goes to pull a way from your side say no firmly if he attempts again stop make him sit then try again. In the beggining this will take a little while the first few days you might only make it a block. But eventually he'll realize I either stay by her side or I don't walk. Don't say the no early it should be right as he feels a pull when he slacks use a treat then eventually your praise word. Once he gets it you can get a longer leash and same concept eventually you can use a retractable leash and he will immeditly come back to heel when called.
As for digging I know it's tuff but until trained you need to watch him at all times but don't let him know that. When he goes to dig call his name or your focus word and the say no sternly. When he does something else praise, goes to dig focus then no. He will get it. Digging is also a sign of boredem. A boxer should get to 45 minute active walks a day. While leash training that will be tough so split it 20 of fetch and 25 teachiung leash manners. As he gets good run him on his leash. Make sure when in the back yard he has plenty of toys. Switch them out for stimulation.
For escaping you need to secure the yard boxers are escape artists. Use your existing fence but build a sub fence into the ground at least a foot to prevent going under if he's going up and under you might want a new fence instead of adding om top and bottom. Keeping him tired will help him stay also and if he isn't fix that can help as well.
For jumping when ever he jumps say no(can be universal for bad like you use your praise word for all good use no or bad for all bad)as you say no turn your body away from him and complelty ignore him. When he calms and stands or sits with out jumping turn back around and praise. Once he has focus and sit down well you can head off a jump by making him sit when you think he'll jump.
For nipping very similar to jumping
With everything just be consistant it seems like a lot but if you do everything right everyday and never let him "get away" with anything you'll be amazed at what a week and then 2 will do. But if you aren't consistant it will take way longer. He needs to know you will not tolerate misbehaving.
Good luck.