There is a whole lot more to responsible breeding than the simple matter of whether or not a particular defect is likely to be passed on - and that you need to ask the question tells clearly that you don't have the knowledge (of genetics and other things) to even be thinking of becoming a breeder at this point. IF you're seriously interested in breeding - which is and should be a serious business, not a hobby or something you'd ever do with a pet dog - then there's plenty of information on this site about the sorts of things you need to learn and the health screening that needs to be done before a dog can be considered for breeding.
Notwithstanding the above, I do commend you for asking (and before, not after, the fact)
As for your actual question, can you breed from a deaf dog - the answer is rather dependent upon why the dog is deaf

. If it is the result of some accident or illness, for example, then there is no reason that the problem would be passed to offspring (i.e. it's not a genetic problem). In that instance, providing the dog is well assessed in the show ring (showing being for the purpose of selecting breeding stock) AND he passes all his genetic screening (for boxers, this means screening for cardiomyopathy and aortic stenosis, hip dysplasia, and hypothyroidism), then there would be no reason at all not to breed from that animal.
If, on the other hand, your dog has been deaf all his life - its a very different matter. It would be very likely in this case that the reason is genetic, and it's those faulty genetics that would be passed to any offspring, who would certainly be at high risk of being deaf themselves or later having deaf offspring.
The most common reason for deafness in boxers, incidentally, is the white coat colour. If you want to know more about the reasons why that's the case, there is a sticky thread at the top of this forum that discusses why white boxers must not ever be bred from, whether they're deaf themselves or not (their ofspring and subsequent generations would be at significantly higher risk of being deaf, creating a problem throughout the breed). Note that the gene causing the problem doesn't only occur in whites (which have two copies of it) but also in flashy dogs (who have one copy). Thus, if you have a dog - especially one with any amount of white - who is deaf from a very young age, then you certainly should
not consider ever using the dog for breeding.