Did you receive dividends from a foreign entity? If so, and they did not issue you a statement you would need to either your records of dividends received or you will need to contact them to find out how much you received.
If you did not receive any foreign dividends, then you will leave this blank or say no you did not receive them.
What if it is part of an ETF or Mutual Fund? What should we enter when asked about "Foreign dividends received?"
The 1099-B from Vanguard only show the foreign taxes witheld.
Usually the Foreign Dividend component is disclosed in a supplementary statement that was included with your 1099 DIV. It is normally reported as a percentage but occasionally there may be an actual dollar amount reported in the statement.
If a percentage, then you would multiply the amount listed in Box 1A on the 1099 DIV by the percentage amount listed in the supplemental form. if you don't find the information listed, you may need to contact your broker to get that information.