You should use a public or serialized List<FeemData> (or an array FeemData[]). Like so:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
[CreateAssetMenu(fileName = "New NeemData", menuName = "Neem Data", order = 51)]
public class NeemData : ScriptableObject
{
[SerializeField]
public string neemName;
[SerializeField]
public string feemText;
[SerializeField]
public Color feemColor;
//Do this
[SerializeField]
public List<FeemData> Feems;
}