League of Legends (LoL) Question: how to..

So if I understand it clearly you want to know how to kill shaco and how to differenciate the real one from the clone?

Shaco is a very slippery clown, from his Q Deceive to his Ultimate Hallucinate he does have a lot of tools to avoid getting killed which might make doing so a really hard task to accomplish.

I recommend you to buy Oracle Lens since it will outline both shaco while he is stealth and disable his boxes.

Others ways to reveal shaco while he's stealth include:

Champions that reveal stealth unities like Lee Sin with his Sonic Wave and Rengar with his Thrill of the Hunt
Twin Shadows
The vision plant, Scryer's Bloom

In the later stages of the game your team should stick together, shaco falls pretty hard late game and isn't able to kill anyone if you give them some peel. Don't let your adc or mid laner alone.

You should also deep ward so you have vision on him when he tries to go in.
Try to invade him if you can, messing up his boxes at level one and invading him in general throughout the game is a very valid plan.

When it comes to find out which one is the real Shaco:

Any debuff like Ignite or Evelynn's Allure will be maintained by the real one but no the clone.
If you use a AOE that damages both shaco and his clone the damage difference should be noticible; the clone takes more damage.
Shaco's close also does less damage, that might be noticible aswell.
Shaco's clone can't use any ability, so if he throws a Two-Shiv Poison at you that's a tell.

Hope this helps