Based on your volume mount of /c/Users/username/Documents/nakama-project/nakama:/data and what you say your contents of C:\Users\username\Documents\nakama-project\nakama\data\modules are then inside your container it’ll look like /data/data/modules if I’m not mistaken.
Your C:\Users\username\Documents\nakama-project\nakama becomes /data inside the container. You probably want to mount /c/Users/username/Documents/nakama-project/nakama/data:/data instead and use a runtime path of /data/modules.