UiUnitAttacher.cs

using UnityEngine;

public class UiUnitAttacher : MonoBehaviour
{
    public GameObject Target;
    private RectTransform _rectTransform;
    // Use this for initialization
    void Start()
    {
        _rectTransform = GetComponent<RectTransform>();
    }

    // Update is called once per frame
    void Update()
    {
        Vector3 pos = Target.transform.position;
        Vector3 vp = Camera.main.WorldToViewportPoint(pos);
        vp.x = vp.x * Screen.width;
        vp.y = vp.y * Screen.height;
        _rectTransform.position = vp;
    }
}