When may you stop here?

This sign means "No stopping" on weekdays ("werktags"). In Germany, "werktags" refers to Monday through Saturday, except public holidays. That means stopping is only prohibited from Monday to Saturday if it's not a public holiday. On Sundays and public holidays, stopping is allowed. That’s why the correct answers are "on Sundays" and "on public holidays." Remember, Saturday is considered a weekday in German traffic rules unless the sign says "Mo-Fr."