Define WHAT you are looking for and WHERE you will look for it.
List keywords for your topic.
What kinds information do you need? Recordings of their work? Books about them? Scholarly articles about them? Newspaper articles? Reviews of performances (live or recorded)? Performer/ensemble web site?
Now select resources which contain the kind(s) of information you need and use your keywords to search.
Discographies are found in books, articles, and more. To find discographies in the Library Catalog, do a subject search for discographies or for discographies Ellington (replace “Ellington” with the last name of the person you are researching.)