The quest of Tea Bowls For Rikyu is easy with marks in the map but the last one doesn't show up.

Where is the 7th Tea Bowl

The last tea bowl is given to you automatically when you complete the Darkness Falls quest.

Darkness Falls is the 55th main quest you get from The Wise in The Shinbakufu category of Objectives.

• If you don't have the quest active on The Wise, you need to progress in the main story a little bit more.