1.If Smeagol turns into Gollum can I trigger any effect of engaging an enemy(if my threat is lower than 30 I can ready Sam,draw a card with Pippin etc.)?

2.If Gollum is destroyed thanks to Legolas ally can I draw a card?

1.Good question, I'm not sure.

2.I believe yes.

1. Yes, he has just engaged you and so you treat it like any other time an enemy has just engaged you.

2. I'm not sure about this one except for when you beat him at the end of Shelob's Lair. Because at every other point he doesn't leave play, he just flips back to Smeagol, so I don't know if it counts as him being destroyed (his text says 'defeated').

1 Yes, in my opinion

2 I would argue that Gollum leaves play as Smeagol enters play

Thank you all!

I believe the rules insert does say specifically that Gollum leaves play and Smeagol enters play, and vice-versa.