there are many theory's but nobody has every been able to give 100% evidence of where it is, if you ask me i think God took it up to heaven with him and if not im sure its in a very very top secret place like in Jerusalem
There have been several claims attributing to the location of The Ark Of The Covenant but, perhaps, the strongest claim is the artifact found in Egypt, in Tutankhamun's Tomb, where the specific description by Howard Carter seems to match with The Art of the Covenant.
I dont think it exists any longer. It held impotance only in the Old Testament. Once Christ came it and the Law it held as holy ceased to be important to such a degree. Most likely the box decayed and the adornments were stolen or repurposed. It was the Law and not the bix itself that were holy after all. The box held the Holy Law but it was just a box