how Does my Deathknell of Scuttle works? My opponet can see my hand during all turn? if i draw a new card, he can see?

It triggers when Scuttle Crab is Killed (sent to trash), not when it attacks — and the effect resolves on the Chain before you establish control or Conquer, so the reveal happens first.

When Scuttle dies, its Deathknell is added to the Chain as a pending item before the card actually moves to the trash, then resolves with the FEPR process. Choose an opponent: they reveal their hand once, for as long as it takes everyone to read it (that's a one-time action, not a standing permission), but "you can look at their facedown cards this turn" lasts the rest of the turn — so a Hidden card they play later is still visible to you. You also gain 1 XP.

Note the timing implication: because the reveal resolves before control/conquer is finalized, your opponent reveals what they have before any conquer happens, and combat cleanup (including healing survivors) has already occurred. Also, since Scuttle Crab is 0 Might, it can still conquer and hold — it just dies to any damage. (Rule 808.1.d; FAQ 10335)

I noticed multiple unrelated questions. I've answered the first one — please ask the others in separate messages so I can give each one proper attention.