here "can't tell" sounds like "don't know". what does "tell" mean here?

Native speaker’s answer
Rebecca
It is kinda similar to "don't know" in this context! Here, "tell" means to decide or determine with certainty. Ex: You can't tell that I cut my hair because It's tied up. Ex: Can you tell that we redecorated? Ex: Jane can tell if anyone's lying to her.