ListChallengeRequest might be what you're looking for. You need to supply a shortCode for the type of Challenge you are looking to get and it's current state. In my Unity project I have a GUI Component that looks like:

public class RunningGameEntry : MonoBehaviour
{
	string challengeInstanceId;
	string userId, facebookId;
	string challengerName, challengerId;
	
	string idOfNextTurnPlayer;
	
	Texture2D profilePicture;
}

Then when I want to update a list of games I write a ChallengeManager which looks something like:

public class ChallenegeManager : MonoBehaviour
{
	public UIGrid runningGrid;
	public GameObject runningEntryPrefab;
	public List<GameObject> runningGames = new List<GameObject> ();
	
	public void GetRunningChallenges ()
	{
		//We refresh running games
		for (int i = 0; i < runningGames.Count; i++) 
		{
			Destroy (runningGames [i]);
		}
		
		runningGames.Clear ();
		
		//We List the challenges called Tic Tac Toe, specifically the ones that are "Running"
		new ListChallengeRequest ()
			.SetShortCode ("ticTacToe")
			.SetState ("RUNNING")
			.SetEntryCount (50).Send ((response) =>
			{
				foreach (var challenge in response.ChallengeInstances) 
				{
							
					go.GetComponent<RunningGameEntry> ().challengeId = challenge.ChallengeId;
					
					go.GetComponent<RunningGameEntry> ().turnStatus = challenge.NextPlayer;
					
					go.GetComponent<RunningGameEntry> ().challengerId = challenge.Challenger.Id;
					
						//Player details are stored in the "Challenged" Collection
						foreach (var player in challenge.Challenged) 
						{
							go.GetComponent<RunningGameEntry> ().challengerName = player.Name;
							go.GetComponent<RunningGameEntry> ().facebookId = player.BaseData.ContainsKey ("ExternalIds");
							go.GetComponent<RunningGameEntry> ().challengerName = challenge.Challenger.Name;
						}
				}
			});
	}
}

The code above is for reference, but you can get the gist of what's going on. If you have multiple game types you can do the same thing but replace the shortCode.

Once you get the facebookId you can get the profile picture with the following function:

public IEnumerator getFBPicture ()
		{
				var www = new WWW ("http://graph.facebook.com/" + facebookId + "/picture?width=210&height=210");
		
				yield return www;
		
				Texture2D tempPic = new Texture2D (25, 25);
		
				www.LoadImageIntoTexture (tempPic);
				profilePicture.mainTexture = tempPic;
		
		}