You can't...since witches don't exist.
england
Elizabeth Guant
brazil
Hansel and Gretel
yes the witch and the bottle is a Myth and also it comes from England
A Witch's companion is often a black cat, or a familiar. A familiar is a creature said to feed from a numb spot on the Witch where the blood doesn't flow. They are said to live on the witch on a mole or wart, that's why witches are often characterized with a wart on their nose.
You ask the person, very nicely, "Are you a witch?" If they reply yes, they may either be joking, or you may have found yourself a real life witch. If they reply no, then move on and pretend you didn't ask. There are no fool proof ways of "spotting" a witch.
Two forms of evidence that New England courts recognized as proof that a person was a witch were spectral evidence and effluvia.
If you are in England then you burned at the stake. If in the US then you where hanged.
London, England
Massachusetts.
1966