Syntax error, insert "}" to complete ClassBody [closed]

You were missing a bracket on the internal if:

package com.gmail.christiangoac77;

import org.bukkit.Bukkit; 
import org.bukkit.command.Command; 
import org.bukkit.command.CommandSender; 
import org.bukkit.entity.Player; 
import org.bukkit.event.Listener; 
import org.bukkit.plugin.java.JavaPlugin;

public class Principal extends JavaPlugin implements Listener {

    @Override 
    public void onEnable() {
        Bukkit.getConsoleSender().sendMessage("§9---------------------------------");
        Bukkit.getConsoleSender().sendMessage("§a         NTE Sex Selector");
        Bukkit.getConsoleSender().sendMessage("§9---------------------------------");
        Bukkit.getConsoleSender().sendMessage("§a           Plugin Activado!");
        Bukkit.getConsoleSender().sendMessage("§a               v1.0");
        Bukkit.getConsoleSender().sendMessage("§e          By: ELPUPAS2015");
        Bukkit.getConsoleSender().sendMessage("§9---------------------------------");
        Bukkit.getPluginManager().registerEvents(this, this);
    }
    @Override 
    public void onDisable() {
        Bukkit.getConsoleSender().sendMessage("§9---------------------------------");
        Bukkit.getConsoleSender().sendMessage("§c         NTE Sex Selector");
        Bukkit.getConsoleSender().sendMessage("§9---------------------------------");
        Bukkit.getConsoleSender().sendMessage("§c        Plugin Desactivado!");
        Bukkit.getConsoleSender().sendMessage("§c               v1.0");
        Bukkit.getConsoleSender().sendMessage("§e          By: ELPUPAS2015");
        Bukkit.getConsoleSender().sendMessage("§9---------------------------------");
    }

    public boolean onCommand(CommandSender sender, Command cmd, String label, String [] args) {

        if(cmd.getName().equalsIgnoreCase("NTEChico")) {
            if(sender instanceof Player) {
                Player player = (Player) sender;
                getServer().dispatchCommand(getServer().getConsoleSender(), "nte player" + player.getName() + "suffix &9♂" );
            } // <--- Agrega el corchete

            return true;
        }

        return false;
    }
}

You are missing a closing key in the second if of the last method

if(cmd.getName().equalsIgnoreCase("NTEChico")) {
            if(sender instanceof Player) {
                Player player = (Player) sender;
                getServer().dispatchCommand(getServer().getConsoleSender(), "nte player" + player.getName() + "suffix &9♂" );

             }// <---------------- Esta llave es la que te falta

            return true;
        }