How to answer the inquiry: "Please confirm that you are not working for another company"

I strongly suggest that you contact the company, because knowing how ELU recommends you interpret this does not ensure you answer it the way they intended. Someone who asks such an ambiguous/poorly phrased question may not have chosen the correct words. You could also ask for advice over at https://workplace.stackexchange.com/

That caveat out of the way, I do have a suggestion.

Since it is not exactly a question as it stands, I found it helpful to rephrase it as one: "Can you confirm that you are currently not working for another company in this field?"

If you are not currently working for another company in that field, the answer is Yes, because you can confirm it. More fully, the answer is "Yes, I can confirm that I am currently not working for another company in this field."

Alternatively, consider that the phrase please confirm indicates that the desired answer is Yes. It's an indication that the asker is checking something they assume to be true/require to be true to proceed.

Other examples:

• Please confirm that you wish to delete this document
• Please confirm that you do not wish to apply for any other positions
• Please confirm that you have a valid work visa or citizenship
• Please confirmed that you are not currently enrolled in school

Same problem here, I've received a questionnaire from my son's school, and this question bugs me a lot: **IF your child WILL NOT be returning for the 21.22 school year?

It's a google form so I don't have place to write yes, he will return. or no, he won't.