If you don't find the option "show the bookmarks bar" in the settings, you have to do this first:
- copy in the adress field: opera://flags/#quick-access-bar
this brings you to the super secret experimental feature "Enables a bookmarks bar below the address toolbar."
choose "enabled" in dropdown menu. default(enabled) seems not to work
now go to settings> User Interface. The check the box "Show the bookmarks bar". It should be there now