" how can i complete this field. I'm trying to fill it in online and then send it via snail mail?"-----> Ok now, I clearly understand your situation; as your spouse is a nonresident alien, you should file either a MFJ or MFS return, your spouse must have either a Social Security Number or an Individual Taxpayer Identification Number. To get an SSN for your spouse, apply at a social security office or US consulate in S.Korea. You must complete Form SS-5.You must also provide original or certified copies of documents to verify your spouse's age, identity or etc.
if your spouse is not eligible to get an SSN( I don't think so , but I am not sure), then she can file Form W-7 with the IRS to apply for her ITIN. In most circumstances, you must submit the Form W-7 with your annual income tax return. Form W-7 submitted without the tax return is routinely rejected by the IRS unless you can show a pressing need for the ITIN. As the W-7 is for your spouse, she must sign it. If it is for your child, you sign the Form as the delegate.
You need send the notarized copy of W-7 to the IRS.
IRS Mailing Address:
Internal Revenue Service
PO Box 149342
Austin, TX 78714-9392
However, as said above, if your wife is eligible for an SSN, then she CANNOT( doesn't need to) get an ITIN; she MUST get an SSN.
+++ +++ I guess TurboTax does not allow to efile if one chooses not to enter SSN info for spouse (married filing seperately). But you can use it to complete the preparation and take printout to file by mail.
Please visit the website for FORM W7 here; http://www.sup.org/authors/forms/W7.pdf Taxpayer Identification Numbers (TIN) U.S. Citizens and Resident Aliens Abroad - Nonresident Alien Spouse