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- James Knowles (murderer), convicted of murdering Michael Donald in 1981
- Sir James Knowles (architect) (1831–1908), British architect
- James Sheridan Knowles (1784–1862), Irish dramatist and actor
- James Thomas Knowles (1806–1884), British architect and father of Sir James Knowles
- Jeremy R. Knowles (1935–2008), chemistry professor at Harvard University
- Jeremy Knowles (born 1981), Bahamian swimmer
- Jesse Knowles (1919–2006), American businessman and politician
- Jo-Anne Knowles (born 1971), English actress
- John Evans Knowles (born 1914), retired Canadian politician
- John Knowles (born 1926), American author
- Julian Knowles (born 1965), Australian composer
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