Ice-Jynx

It will do the job, but you will need to dance and dodge.

For attacking, bad IV but good moveset will do the job. The IV will not do a lot in the battle - a decent stamina stat for Cloyster would be the important bit.
Train up that Cloyster and use that.

The short version - bad IV good moveset Cloyster is your best bet.

EDIT PC/P Alakazam is a beast - again a decent stamina stat and that moveset and I would power it up all the way(I even have one with bad stamina...he needs to dodge well).
...but both. The Cloyster with a good moveset and the Alakazam on PcP should both be included in a good attacking selection when choosing your roster.
Leave Jynx...go the Alakazam and Cloyster, and you won't regret it.

I have a pair of Ice Jynx both around 1700 CP that I use to both to prestige against Dragonites as well as to take them out. With dodging most attacks (including Quick attacks) I can take down about 1 1/2 3000 CP Dragonites.

Neither works as well as my Lapras, but he's sometimes in a gym. Once I get a cloyster with the proper move set, I imagine I'll use that as well.

HTH

Steel is strong against ice, but weak against water. So you wouldn't want to use jynx against a dragonite with steel wing, while you could use cloyster, lapras, or dewgong.

Personally, I prefer the stats of cloyster anyway, and the candy is pretty easy to find where I am. You could try jynx a non-steel wing dragonite and see how you like her.

Just do it

Ice Punch is meh. Being 3 bar doesn't mean much since you'll be gaining energy faster than you can use it if you're dodging every attack, which you probably will be since Jynx has low HP. The only thing that matters is it's cooldown, which is on par with Ice Beam and Blizzard but does the lowest damage of the 3.

I found myself not using Ice Punch that often, usually only twice per fight as it would mean missing dodges, and I could get more damage with less HP spent from using several Frost Breaths and dodging instead.

I have a Ice Shard + Blizzard Cloyster and I'd rather use that instead of an Frost Breath + Ice Punch Jynx. Ice Shard and Frost Breath do similar DPS and I don't find Ice Shard makes dodging difficult against Dragonite, I can comfortably fit in 1 Ice Shard per Dragon Breath and 2 per Steel Wing, but Blizzard's a much better charge move because you can use it to finish off the Dragonite from a much higher HP and negate the downside - getting hit by a charge move during the damage delay.

Usually I prefer lower cooldown moves but the cooldown difference between Ice Punch and Blizzard (or Ice Beam and Blizzard) is much closer than say, Petal Blizzard and Solar Beam that there's fewer situations where you'd miss a dodge with Blizzard where you wouldn't with Ice Punch or Beam, so I prefer having the extra damage.