You will need to contact your spouse and ask if he/she is itemizing or using the standard deduction and at minimum you will need to enter his/her social security number.
If you live in a Community Property State, you will need to his detailed income and deduction information as well.
If you are unable to contact your spouse or your spouse is not cooperative you will need to include a statement, along with your return, to that effect, and your return will need to be mailed to IRS.
Here is information regarding filing a separate return in a Community Property State: Community Property MFS
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