If you find out that your ancestor worked in one of the professions there are various places you can look for sources.
Professional people are likely to have been educated at university.
Details of people who attended Oxford and Cambridge universities can be found in either the Alumni Oxonienses or Alumni Cantabrigienses. Similar publications exist for Dublin and the ancient Scottish universities. The information given is the name of the father, his rank and occupation, where the student lived, his college and some details of his later career. You will find copies at some large reference libraries and record offices. The majority of local professional people would have had their details included in trade directories either in the list of private residents, or in the commercial section under the name of their profession, or both.