So this doesn't require concentration like the conjure elemental spell?

Correct. The gem is also destroyed in the process. So it is a limited use item.

Does it take an action or bonus action to command the elemental? Or is it independent and takes its own turn without instructions?

Since the item doesn't specify it takes an action or bonus to command it does not,  "Talking" or in the case "Commanding" is a free action so one could command the elemental without any expending any action resources. 

The rules specifically say that It takes its own turn immediately after your turn, so it is independent and it does take is own turn.  However "without instructions" is probably NOT true.  If it didn't receive instructions from its controller presumably it would just do nothing or maybe something that an elemental might do on its own. 

In practice in my games when I DM, I just let the player control the creature however they like.   However,  the DM could also assume control of the creature, and it would only follow the exact instructions that the player vocalizes to it.  "Move here and attack that thing"  "Dash to this location and wait further instructions"  It would depend on the DM and how powerful and how much freedom they wanted to give the magic item and player.

When you take a Utilize action to break the gem

This is an action to summon it. Utilize action.

So it looks like in DMG`24 it doesnt need concentration? Thats a big boost :D I like it :D