WoWDB

Going for achievements? You can earn treasure maps by doing the main storyline in the WOD quest areas (IE: Completing Nagrand main storyline gets you the treasure map)

The treasure maps will mark your default map UI for treasures. You can buy the maps (once you've completed the storylines from zones you want maps from) from either

Srikka (Horde in Warspear)

Grakis (Alliance in Stormshield)

You can also earn the maps from the Garrison missions, they appear to pop up randomly if you're eligible for the maps and haven't purchased them.

Alternatively, you can download an addon named handynotes https://mods.curse.com/addons/wow/handynotes

And then install the Draenor treasures ( https://mods.curse.com/addons/wow/handynotes_draenortreasures )

(Note: It appears the Draenor treasures hasn't been updated in some time.)