Unfortunately, your options may be limited.
If you were separated for at least the last 6 months of the year (since July 1) then you can file as head of household. This is very easy and you do not require any information from your spouse, not even their SSN.
If you do not meet the "last 6 months rule" then you will need to file as married filing separately. (I am taking married filing jointly right out of the discussion due to the protective order). With married filing separately, the only information you need from your spouse is their social security number. If you don't know it, ask your attorney to get it from their attorney. If you still can't get it, you will have to file by mail. Leave the place for the spouse's SSN blank, print your return and sign it, and attach a written statement explaining the situation and giving any details you can (name, address, birth date, etc.). When filing separately, you don't need any other information from your spouse. You don't need their income or their deductions.
There is a chance you can file as head of household even if you did not separate until after July 1. You can file as head of household if you are "considered unmarried" for legal purposes for being "Legally separated from your spouse under a divorce or separate maintenance decree."
The problem here is that I have never found a tax court case or state law that was actually accepted by the IRS as allowing you to be unmarried when you are still legally married. I remember reading two cases from NY and NJ, and in those states, there is technically a "permanent legal separation" on the law books, but no one uses it any more, it's a holdover from the days when divorce was rare and socially unacceptable. It created a status that guaranteed the spouses complete legal and financial freedom from each other except they couldn't remarry (which is why no one uses that status any more). A regular legal separation on the way to a divorce did not meet the IRS qualification even if it was under a judge's supervision.
Your state law may be different, but I would ask for advice from an enrolled agent (an accountant specially approved to practice before the IRS). Divorce attorneys and judges are often badly uninformed on the IRS rules surrounding divorce. You can also try filing as HOH and hope your aren't audited; if your spouse files as married filing separately (as they are required to do) and you file HOH, it probably won't raise any red flags.
