Dunno, it's wrong to write "I don't know" in professional or academic writing. You'd have to write in academic writing.
Dunno is actually the slang word for the word "I don't know" and sometimes it is spelled the way it is sometimes spoken "I don’t know."
You will probably come across both of these writing styles at various points in your life because academic writing and professional writing are so drastically different from one another.
To learn more about Professional or Academic writing here
https://brainly.com/question/18259028
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