This is the sarcophagus of Saint Nicolas, behind safety glass. It's in room 7, the southernmost aisle.

The sarcophagus is a re-used sarcophagus of an earlier occupant, that has been smashed at some time, probably when the Bari merchants robbed the grave.

At a site (www.stnicholascenter.org), dedicated to the saint, as part of a discussion that several tombs have been seen as the one occupied by the saint, one can find "... often identified as the original tomb, as the side is smashed, however, the cover shows two figures, neither a clergy person."