If my father in law is deceased, What do I enter for current address?

Enter the address where you want the IRS to send any notices or letters about the tax return, and a mailed refund check, if any.

If you are preparing his Tax Return you must first go to his personal file page and enter the Date of Death.  Then for address you should show your address, so that the IRS can send any mail if necessary to who prepared his last Tax Return.  Unless there's another family residing at his last address, that can respond to any notices from the IRS.

You can also go to the IRS website www.irs.gov, and place your question in the search dialog box.