If I'm wondering about duplicates existing for a modern name that follows modern American formats, i.e. Jackson Day, I just put it in the WikiTree's search bar at the top of the page and trust the results.
If it's a person who may have used a variety of names, I use Google Advanced Search, put WikiTree in for one of the qualifications, and add in all the other combinations I can think of. Google Advanced Search has sometimes found duplicate persons for me on WikiTree I would never have found using other methods.