Guild Wars 2

Q1 does air 25 have an icd
Q2 if you use sigil of vuln can yoy apply 2 stacks at once.
Q3 if not, can water scep auto prco both being 3 individual attacks
Q4 is the sigil of vuln better the inc vuln duration?

1 – i don’t think weak spot has an icd.
2 – yes. and fyi, shard of ice(water ii) with arcane power will let u apply up to 6 stacks of vulnerability at once if u use dagger auto-attack in water attunement
3 – i think Ice Shards auto-attack does count as 3 individual attacks
4 – i might have to say that the 25minor air trait(weak spot) is better b/c of higher proc chance.

For the last question im asking about sigils, is the duration sigil better or is the apply on crit better. the 10% duration makes a 5 sec stack to 5.5 sec?

The sigil of frailty (on-crit) is better

Q4: depends upon a number of factors. Could you elaborate?

Also check this post of mine:
https://forum-en.gw2archive.eu/forum/professions/elementalist/Zelyhn-s-Advanced-D-F-PvE-Guide/page/4#post3091832