If your per diem is included in your wages, you can enter that amount and deduct it. If it is not reported as wages to you, you cannot deduct the cost.
Depending on what your per diem covers, there may be additional out-of-pocket costs that you can deduct. Please see the link below.
Also, it has to be a temporary job location that is expected to last for less than one
year to deduct it.
You didn't say if you were an employee or self-employed. I'll assume you are an employee (receiving a W-2). I'll post the instructions below for you.
"Travel expenses paid or incurred in connection with a temporary
work assignment away from home are deductible. However, travel expenses paid in
connection with an indefinite work assignment are not deductible. Any work
assignment in excess of one year is considered indefinite.
Also, you may not
deduct travel expenses at a work location if it is realistically expected that
you will work there for more than one year, whether or not you actually work there
that long. If you realistically expect to work at a temporary location for one
year or less, and the expectation changes so that at some point you
realistically expect to work there for more than one year, travel expenses
become nondeductible when your expectation changes."
Travel Business
Expense
http://www.irs.gov/taxtopics/tc511.html
Below are the steps to enter
your qualified job-related expenses into TurboTax. These expenses go on Schedule A Itemized Deductions where they are subject to
the 2% of adjusted-gross-income limit. This means only the amount over 2%
of your adjusted gross income will be deductible on the Schedule
A. If you have enough expenses, and typically itemize
your deductions, it may benefit you.
Where do I enter job-related expenses?
https://ttlc.intuit.com/replies/4800418
