For this achievement, you basically have to find all the Jani items and hand them in at her piles. Now, I didn't know there were a few hidden things with this achievement...
The first thing was that there is a chest that appears in Dazar'alor near one of the bridges over the waterfall down the pyramid. I went looking for it after I got the achievement but couldn't find it, but 2 days later when I logged in I saw it on the minimap!
There was an item in it to scrap, and when you scrap it, a new quest pops up which allows you to talk to Jani and you can turn all your Jani piles into scrappers! Before and after shots (where they turned a statue into a Jani pile)...
It also allows you to buy a pet from Happy Holaua in the pet battle section of Dazar'alor. Hello Child of Jani!