It's easy to instantiate prefab in Unity via Houdini Engine. But I wonder how can I view the prefab inside Houdini. I know it can be done by export Unity prefab as fbx and import in Houdini with File node and attach to some materials but it's not efficient.
Is there some node that you can input the path of the prefab and so it can read the mesh and generate the material?

You can expose a object path parm on your HDA, which will then create an input field in Unity. You can then set your prefab as the input object for that input field, which will then upload the mesh and material assignment into Houdini.

Read the input section: https://www.sidefx.com/docs/unity/_inputs.html [www.sidefx.com]