First a precision: the concept of assets only exist at design-time. At runtime you have contents.
A scene (or a prefab) contains essentially entities. Your terrain model will be assigned to a model component on one entity in your scene. What you need to do then is to find your entity and get its component.
To find a entity by name, you can for example start from the root entities and iterate through the scene tree:
var scene = Entity.Scene;
var myTerrain = scene.RootEntities.DepthFirst(x => x.GetChildren()).FirstOrDefault(x => string.Equals(x.Name, "MyTerrain"));
var modelComp = myTerrain?.Get<ModelComponent>();
var model = modelComp?.Model;
I did not detail the
DepthFirst() utility method. Basically it is like its name implies and depth-first iteration of the tree using the
GetChildren() extension method to get the children entities of a given entity. You can implement a breadth-first search if you prefer, it doesn't really matter.
Of course this is highly inefficient. A better way would be to have a script with an
ModelComponent property that you could assign from the scene editor in the GameStudio. Even if your model is say generated at runtime, you can already place an empty entity in the scene at design time and reference it in a script.