I have a tropical snow plant and it has stopped growing. I know it's winter time but I keep the room warm and it gets sun light. It has been 2 month the new leaves have not open. And I have a plant light plus I give it plant food.
Over watering is often times the biggest issue for a Dieffenbachia.
Soil should be moist, but never soggy.
Your plant will do well in a bright and filtered sunlight setting.
The pot that you have looks a bit large for the size plant that you have.
To large of a container can lead to overwatering and root rot.
I would suggest lifting the plant and inspecting the roots. You can prune away any dead roots and then plant the plant into a smaller and better sized pot.
Use a good quality potting soil.
Here is a link with more information.