A client is asking us for cost breakdown on a job and wants us to include how much profit we will be making on the job. Are they legally allowed to ask us that? They owe us money and have implied that we won't get paid unless they know who much profit we made on the job.

They may ask, you are not required to tell them. If they don't pay let them know that you would hate to have to sue them.

Example, if you installed a rug, your statement to them for example shows their cost, not yours, if you paid 400 for the rug, and changed them 800, you show a itemized statement of rug at 800. You are not required to provide your cost