How does the artist use tenebrism in the piece above?

By the pose of the human and the dark background.

Explanation:

Tenebrism, from Italian tenebroso ("dark, gloomy, mysterious"), also occasionally called dramatic illumination, is a style of painting using especially pronounced chiaroscuro, where there are violent contrasts of light and dark, and where darkness becomes a dominating feature of the image.

By bringing out the stark contrast between the saint and the background.

Explanation:

got 100 in the practice : )