AssetDatabase.GetAssetOrScenePath

Description

Returns the path name relative to the project folder where the asset is stored.

All paths are relative to the project folder, for example: "Assets/MyTextures/hello.png" When a game object is part of a Scene, the Scene path is returned.

using UnityEditor;
using UnityEditor.SceneManagement;
using UnityEngine;
using UnityEngine.SceneManagement;

public class AssetDatabaseExamples : MonoBehaviour
{
    [MenuItem("AssetDatabase/Get Asset Or Scene Path Example")]
    static void GetAssetOrScenePathExample()
    {
        var asset = AssetDatabase.LoadAssetAtPath("Assets/Prefabs/Cube123.prefab", typeof(GameObject));
        //This will output Assets/Prefabs/Cube123.prefab
        Debug.Log(AssetDatabase.GetAssetOrScenePath(asset));
        var clone = Instantiate(asset);
        EditorSceneManager.SaveScene(SceneManager.GetActiveScene());
        //This will output Assets/Scenes/SampleScene.unity
        Debug.Log(AssetDatabase.GetAssetOrScenePath(clone));
    }
}