My husband started a business last year, a single member LLC, as a personal trainer/private coach. How do we report/deduct free sessions done for potential clients?

[Opus 17 · Accepted solution]

You don’t.  Your tax “reduction” is the fact that you have less taxable income to pay tax on.  You can’t take a deduction off of revenue you never got.  

[nieboer2010]

So it’s not considered a “loss” for that time he spent which he could get paid for by training a paying client?

[Opus 17]

The "loss" is that you don't get paid.  And therefore you don't pay tax on what you don't get paid.
If he incurred costs, like gym fees and travel expenses, for those clients, those expenses are still deductible business expenses.