I'd like to know in which situations can we use already in a question. This question appeared in my English book "What wildlife has she seen already?"I've always been taught that we use yet in questions and already in affirmative sentences. Another point is: isn't already supposed to be in the middle of the sentence???I'm so confused...
'Already' commonly appears in questions such as the one you have given.

Not a rule, but a guideline: 'already' commonly appears in affirmative sentences (questions and statements), and 'yet' commonly appears in negative sentences (questions and statements). This is not absolute, though.