IRequirement.cs

public interface IRequirement
{
	bool IsComplete {get; set;}

	void OnRequirementEvent(IRequirementArgs args);
}

TalkArgs.cs

public class TalkArgs : IRequirementArgs
{
	public string npcName;

	public TalkArgs() { }
	public TalkArgs(string npcName)
	{
		this.npcName = npcName;
	}
}

TalkRequirement.cs

public class TalkRequirement : IRequirement
{
	private string npcName;
	public string NpcName { get { return npcName; } }

	private bool isComplete = false;
	public bool IsComplete
	{
		get { return isComplete; }
		set { isComplete = value; }
	}

	public TalkRequirement() { }
	public TalkRequirement(string npcName)
	{
		this.npcName = npcName;
	}

	public void OnRequirementEvent(IRequirementArgs args)
	{
		if (args is TalkArgs)
		{
			var talkArgs = (TalkArgs)args;
			//Do Stuff
		}
	}
}