What is Can I Speak To You Son?
1.
If your dad is cool and he says it, he's pulling you aside to have a confidential "coaching" moment, while saving you the embarrasment of having your friends hear the whole subject.
Can also be said to someone about your own age who is being a bit naive, for example about a girl who might be bad news, but who your homey is starting to get caught up in. You might say to him "can i speak to you son" as a way of letting him subtly know he might want to talk to you because there might be something you know that he might want or need to know.
Your unsuspecting friend: "Man, I don't see why all them other dogs be saying that girl is a
golddigger ! She seemed nice, and very interested in me."
You: "can i speak to you son"
2.
If said by
"I suspect you are doing drugs. Can i speak to you, son?"
See