Which organelle should be listed under “animal only” in the diagram? nucleus centriole ribosome cell wall

From the listed cell organelles/structures, only one that's almost "Animal Only" is the centriole. The nucleus is widely found whether in animals, plants or other eukaryotes. The ribosome is also found in any cell. The cell wall is not present in animal cells. The centriole, although may be present in other specific types of cells, it is always present in animal cells, being a characteristic of such.
Centrioles are important for the organising of the mitotic spindle, for cytokinesis, for sperm movement being part of the formation of the flagellum, and others.