How do I ask for payment under the table?

You ask for under-the-table payment by mentioning how you'll be paid in an interview. If the interviewer doesn't come right out and say that you'll be paid off the books, you do have the option to pry further and say that you prefer to be paid in cash. However, it isn't recommended.

Being paid under the table is a grey area in the professional world. It can be a big turn-off for an employer if you're asking to be paid this way, so it's best just to go searching for a different position if you aren't offered to receive under-the-table compensation.