(covers information from several alternate timelines)
Denkir was a location.
In 2366, in an alternate timeline, during the Federation-Klingon War, Denkir's position was labeled on a tactical situation monitor in the ready room aboard the USS Enterprise-D. (TNG: "Yesterday's Enterprise", okudagram)
This location was only mentioned in writing.
Two of his paintings depicted the planets Denkir II and Denkir IV from the perspective of their moons. These paintings were displayed on the walls of the Enterprise by the set decorator during TNG's first season.