It just comes down to proving that you can drive the necessary metrics for the job (i.e. Key metrics for a sales person would be revenue, for a designer it might be boosting retention).

What could it be for an attorney? Winning cases? Getting more clients?

Once you know what the key metrics are, you can choose one of the above options to prove that you can drive that metric — you don’t necessarily need to recreate the job on your own if you can’t.