NetworkView.owner  

function OnNetworkInstantiate (info : NetworkMessageInfo) {
    if (!networkView.isMine)
        Debug.Log("New object instantiated by " + networkView.owner);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void OnNetworkInstantiate(NetworkMessageInfo info) {
        if (!networkView.isMine)
            Debug.Log("New object instantiated by " + networkView.owner);
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def OnNetworkInstantiate(info as NetworkMessageInfo):
        if not networkView.isMine:
            Debug.Log(('New object instantiated by ' + networkView.owner))