CSHARP

unity button press onclick click add C#

using UnityEngine;
using UnityEngine.UI;

public class Example : MonoBehaviour
{
	[SerializeField]
    private Button button;
    
    void Start()
    {
    	button.onClick.AddListener(RunThisTask);
    }
    
    void RunThisTask(){
    	//do something
    }
}

unity button onclick

GetComponent<Button>().onClick.AddListener(()=>print("clicked"));

unity onclick object

using UnityEngine;
using System.Collections;

public class Click : MonoBehaviour {

    public GameObject gameObjectToClick;
    void OnClick(){
         gameObjectToClick.SpecialFunction(); //call special function you wanted to call
    }
}