A dockmaster was a person who was responsible for the docking procedures of an outpost.
In 2151, an alien dockmaster informed Captain Jonathan Archer and Sub-Commander T'Pol that a Klingon K'toch-class scout ship had visited his trade outpost on Rigel X seven days beforehand. While in his control tower, the alien dockmaster monitored the approach vector of Elkan Nine. (ENT: "Broken Bow")
In 2152, a Markalian served as the dockmaster of a trading dock on Pernaia Prime's moon. (ENT: "The Seventh")
In 2154, Captain Erika Hernandez of the NX class starship Columbia requested clearance to depart from the dockmaster of Starfleet's drydock. (ENT: "Affliction")
In 2293, Captain James T. Kirk asked Commander Uhura to hail the dockmaster, so the USS Enterprise-A could depart from spacedock. (Star Trek VI: The Undiscovered Country)
A dockmaster aboard Deep Space 9 had an office on the Promenade. (Star Trek: Deep Space Nine set decoration)