This allow us the position text elements over world objects, With screen overlay, on prefabbed things. Tags are required on the elements to find at runtime.

GenerateTextObjectAndPositionDuringRuntime_FOR_PREFABS.cs

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class GenerateTextObjectAndPositionDuringRuntime_FOR_PREFABS : MonoBehaviour
{

    public string CanvasToPopulatesTag;
    public string TextPrefabTag;

 
    private GameObject instantiatedPrefab;
    private Text textObject;
    private RectTransform rectReference;

    public int FontSize;

    public float LabelVerticalOffset = 0f;

    public string textToDisplay;

    bool draw = false;

    void Awake()
    {

        if (OverlayReferenceHolders.OverlayCanvas == null)
        {
            OverlayReferenceHolders.OverlayCanvas = GameObject.FindGameObjectWithTag(CanvasToPopulatesTag);
        }

        // populate from the scene since we are struggling...
        if (OverlayReferenceHolders.TextPrefab == null)
        {
            OverlayReferenceHolders.TextPrefab = GameObject.FindGameObjectWithTag(TextPrefabTag);
        }

    }


    void Start()
    {

        if (OverlayReferenceHolders.OverlayCanvas == null)
        {
            OverlayReferenceHolders.OverlayCanvas = GameObject.FindGameObjectWithTag(CanvasToPopulatesTag);
        }

        // populate from the scene since we are struggling...
        if (OverlayReferenceHolders.TextPrefab == null)
        {
            OverlayReferenceHolders.TextPrefab = GameObject.FindGameObjectWithTag(TextPrefabTag);
        }

        instantiatedPrefab = Instantiate(OverlayReferenceHolders.TextPrefab);
        textObject = instantiatedPrefab.GetComponent<Text>();
        rectReference = OverlayReferenceHolders.OverlayCanvas.GetComponent<RectTransform>();
        instantiatedPrefab.transform.SetParent(OverlayReferenceHolders.OverlayCanvas.transform, false);
        textObject.text = textToDisplay;

        if (FontSize > 0)
        {
            textObject.fontSize = FontSize;
        }

        textObject.enabled = false;
        draw = false;
    }

    void OnBecameInvisible()
    {
     
        textObject.enabled = false;
        draw = false;
       
    }
    void OnBecameVisible()
    {  
        draw = true;

    }

    // Keep it centralised.
    void Update()
    {
        MoveObject();
    }

    private void MoveObject()
    {

        if (!draw)
            return;
       
            Vector2 pos = WorldToCanvasPosition.ConvertWorldToCanvasPosition(rectReference, Camera.main, transform.position);
            textObject.rectTransform.position = new Vector3(pos.x, pos.y + LabelVerticalOffset);
            textObject.enabled = true;

    }
}