Knaak is a surname. Notable people with the surname include:
- Delores J. Knaak (1929–2020), American educator and politician
- Fritz Knaak (born 1953), American lawyer and politician
- Peter Knaak (born 1942), Canadian politician
- Rainer Knaak (born 1953), German Chess Grandmaster
- Richard A. Knaak (born 1961), American novelist
- Turid Knaak (born 1991), German footballer
- Will Knaak (born 1984), American guitarist and singer-songwriter