Divorced in 2016-filing as HOH.In 2015Filed MFJ and itemized.Turbo tax asks for data from 2015 filing.Do I provide 100%data even though it relates to 2 people?why needed?

There are several reasons you might be asked about last year.  If you are being asked about business (employee business expenses or self-employment expenses, like assets, use of a car, etc.) then each business is specific to the person, not the joint return, so you would answer about your business or job.

The other common reason is a state income tax refund.  A state income tax refund that was paid in 2016 is taxable income if,

1. you itemized deductions last year

2. and you deducted state income taxes that were taken out of your paychecks on your W-2s

3. and your itemized deduction, if you subtract the amount of the refund, is still more than the standard deduction.

However, the state tax refund is only taxable once, so it might be your income (if you kept it all) or your ex's income (if they kept it all) or it might need to be split (if you split the refund, or if it went into a joint account before you separated).  Between you and your ex, someone needs to report the state tax refund as income.