The Yokai this Trophy refers to are the: "Nurikabe" and "Mujina".
Nurikabe are the fake walls you find throughout Nioh, and Mujina being the Mimic chests.
To communicate with either of them it refers to using a gesture in front of them;
The Nurikabe only need to have one gesture used on them with the right corresponding color, which is random. It doesn't have to be a certain gesture just the right color needed at the time. So it's always best to do Red and Yellow which gives you 66% chance of getting it right if neither work let it kill you and come back and use a Blue gesture. Once the Wall disappears it will count as a successful "communication".
Using the walls is the fastest and easiest method to farm, especially in the Kyushu Region on the 2nd Main Mission: "Deep in the Shadows" where once you enter the first cave where the bats swarm at you and through the first door on the bottom floor it is in the back corner of the room. Use a "Himorogi Branch" and reload the mission.
For a visual representation of this method, video courtesy of PowerPyx:
Like I said before you can do it with the Mimic Chests, just requires more effort.
When opening the chest, the Mimic will stun you and knock you down. It will then imitate you and clone itself but before trying to kill you it uses a gesture and wait a good second. You must mimic the gesture to successfully "communicate".
Best place I found was the 5th Sub Mission: A Request From Ginchyo (Kyushu Region)
Two Mimic Chests are in this level;
The first is right when you start the mission in the First Hut and this Mimic requires you to use the Red Gesture; "That's Not Good".
The other is right above this one in the big hut, the chest on the left is the mimic and requires the Blue Gesture, "Clap".
Just like Nurikabe you can use the "Himorogi Branch" and redo the mission to farm these.