Uncle Mako can be located chilling at the VIP island of the newly-added Valdrakken Hot Springs in Thaldraszus, meditating by a table served with tea.
The NPC serves as a double homage: First to the Avatar: The Last Airbender character of Iroh, a retired Fire Nation general, Firebending master, and mentor to Prince Zuko. Uncle Mako shows several similarities to Iroh: