WatchlistSymbolAddedEventArgs

 using cAlgo.API;
 namespace cAlgo
 {
     // This sample shows how to use WatchlistSymbolAddedEventArgs
     [Indicator(IsOverlay = true, TimeZone = TimeZones.UTC, AccessRights = AccessRights.None)]
     public class WatchlistSymbolAddedEventArgsSample : Indicator
     {
         protected override void Initialize()
         {
             Watchlists.WatchlistSymbolAdded += OnWatchlistSymbolAdded;
         }
         private void OnWatchlistSymbolAdded(WatchlistSymbolAddedEventArgs obj)
         {
             Print("Symbol {0} Added to Watchlist {1}", obj.SymbolName, obj.Watchlist.Name);
         }
         public override void Calculate(int index)
         {
         }
     }
 }

 import clr
 clr.AddReference("cAlgo.API")
 from cAlgo.API import *
 class Test():    
     def initialize(self):
         api.Watchlists.WatchlistSymbolAdded += self.on_watchlist_symbol_added
     def on_watchlist_symbol_added(self, args):
         print(f"Symbol {args.SymbolName} Added to Watchlist {args.Watchlist.Name}")