Sentence examples for don't know from inspiring English sources

"don't know" is considered grammatically correct and can be used in written English.
It is a contraction of "do not know" and is commonly used in informal and conversational writing. Examples: 1. "I don't know what to do next." 2. "She said she's not sure, but I don't know if I believe her." 3. "I've never been to Paris, so I don't know much about the city." 4. "Don't worry, I don't know anyone here either." 5. "I'm sorry, I don't know the answer to that question."