Unexpected Symbol }

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.UI;

public class mainMenu : MonoBehaviour {
public Button Play;

// Use this for initialization
void Start () {
	Button playButton = Play.GetComponent<Button> ();
	if(playButton.onClick.SceneManagement("load"))
	}


// Update is called once per frame
void Update () {
	
}

}

Any ideas?

line 5, remove the extra brace } from the if statement or add an open brace { above it since you will likely want to add a body to the if statement in the future.

Line 5 closes the Start method.
On line 4, you have an If statement with nothing, you need opening and closing curly brackets.

public class mainMenu : MonoBehaviour
{
    public Button Play;

    void Start ()
    {
        Button playButton = Play.GetComponent<Button> ();
        if (playButton.onClick.SceneManagement("load"))
        {
        }
    }
 
    void Update ()
    { 
    }
}