It's quite a hard word to explain. "He has the uncanny knack (skill) of coming to my house to say "hello", just when we are ready to eat. I always feel I must invite him to join us." "Uncanny" means "hard to explain" and perhaps also a bit suspicious. But it's not very negative. You say it when you are wondering about something which is not normally very serious. It is used with words such as skill, ability, knack.