So I'm doing readworks questions in class I have have to give a character trait but I don't know what you call someone that is always wrong.....
If such a person is reliably always wrong, you may call them a contra-indicator. This is sometimes used in financial markets. You may not know what to do, but then you look at what the contra-indicator does, and you do the opposite for virtually guaranteed success.
Unsound (adj.) feels like it might work.
Not dependably strong or solid.
Not physically or mentally healthy.
Not true or logically valid; fallacious: an unsound conclusion.
Depending on the context, I'd feel confident in the wrongness of someone described as unsound.