Beginning Reading

Sophia is starting to learn how to read. While she and I sat down to read one of the kindergarten take home books, she stumbled across a new word...

Soph: Kuh-noh-uw....kuh-nohw **She crinkled up her face and looked at me questioningly.**
Me: It's "know." Like "I know you."
Soph: **Looking from the book and me** But--there's a "k."
Me: Yes, there is. But this word has a silent "k."
Soph: **exasperated** So how am I supposed to know which words have a silent "k"???