The place where you are asked why you wanna work for emirates is on the online application form. Of course you need to read all the website and know in genereral the destinations they fly too, but dont worry they wont ask you specific questions.
Then for the group assesment day, the group topics are not really related to Emirates. It can be like: ok talk to the person to your left for five minutes and describe that person to the group then. Or: if you made a play, what kind of a play would it be and why? then you gotta discuss it with the group.
as for weaknesses they dont really ask that. What they most likely do in the final interview is asked about situations you had to face at work in the past. Like «tell us a moment where you tresspassed a rule, what happened, what did you learn from it?» Then, they might ask you: Talk to us about a stressful event in your previous job? or tell us about a time when you disagreed with a coworker and got in a fight, what happened?
you see what i mean? so before the last interview write down on paper the situations that happened in your previous jobs so you are ready.
Untill that last step, the final interview, be positive, SMILE A LOT, talk to the other people doing the process with you, you might make friends that will go to Dubai with you and it will make you less nervous for group discussions.
good luck
I hope it answered your question a little bit
Carine