
They will either be deaf or not it isn't progressive deafness.
There is a high likelihood of a white Boxwer being deaf which is why in the past breeders prefered to put them to sleep at birth, as there was no sure way of checking until it became apparent (usually due to behavioural and training problems) that they were in fact deaf.
Any responsible breeder will take their whilte pups to be BAER hearing tested (they use electrodes to check if the impulses are being registered by the ear), this can be done from 5 weeks of age(same test as for babies that fail the routine tests for hearing at the doctors, as my perfectly hearing son did :D )
I would not contemplate buying the pup unless he has been BAER tested, no other test is reliable.