You can start by looking at your father's income tax returns for the past five years. If he was earning interest or dividends from bank accounts, stocks, mutual funds or other investments, you will find them listed on the returns. Also, if he sold investments in the past, you will find a record of those sales listed in the returns. Not all investments generate income or losses, though. Therefore, you should also look through his records to see if he owned other properties.
Most people have a desk or file cabinet where they keep their records.
You should make a list of all the bank accounts, brokerage accounts, houses, retirement plans and other investments he owned. When your list is complete, you can contact each company, bank or broker to inquire whether the investments still exist. If the particular investment is real estate, you can call a title company to see if he is still the owner. Many counties have their real estate records available on the Internet, so you may want to look there, too. However, unless you are the executor of your father's estate, you will probably not be too successful in learning about the status of your father's accounts and other investments.