How do I teach my kid work ethic?

Not by talking about it, and mostly not by assigning more of it either.

Work ethic is usually described as a character trait, which makes it sound like something a kid either has or needs to be given. What it actually looks like from the inside is a belief: that effort connects to outcomes in a way you can feel. A kid who has never seen that connection has no reason to work hard, and no amount of describing it will install it.

The connection is what has to be visible, and a few things make it visible faster than anything else.

Work somebody chose to pay for. Chores get done because you said so, so the effort connects to your approval rather than to anything real. A neighbor handing over twenty dollars connects effort to a result that had nothing to do with whether anybody loves them.

Doing it on a day they did not feel like it. This is the actual skill and it arrives around week five or six of anything. The first customer is exciting and the fourth is just Saturday. A kid who turns up anyway has learned the thing that shows up in every job they will ever have, and it cannot be taught in advance.

Getting better at something measurable. The job that took two hours takes fifty minutes. That is effort becoming visible, and it is more persuasive than praise.

What works against it: rescuing. Every time an adult quietly fixes a missed job or covers a mistake, the connection between effort and outcome gets cut. The lesson that lands instead is that outcomes are managed by somebody else.

And when it does show up, name the right thing. You figured that out yourself rather than you made forty dollars. The money is evidence. What you want them to notice is what it is evidence of.