Autosomal DNA (auDNA) testing can provide clues. You don't have auDNA from all your ancestors and so you may actually have Native American or African ancestry somewhere in your ancestral tree but not have it show up in your auDNA results. On the other hand, if you know (or suspect) a living relative who is a direct paternal line descendant or a direct maternal line descendant of your likely Native American or African ancestor then you can easily confirm the (continental) geographic origin of the ancestor's direct line with a Y-DNA test (for direct paternal line) or a mtDNA test (for direct maternal line).