Very much depends on what level you are.
Takish-Hiz (North Ro) has the best plate from LDoN. That is good if you are 60 but if you are level 25 1492 point items are pretty irrelevant. Rujarkan has plate starting at 48 points for low levels and Mistmoore has 150 point plate.
As far as which is best for an SK I don't think it matters. unlike Paladins there is no big advantage to tackling undead. You might just use your undead Lull to pull the same way paladins use pacify I suppose. You have snare so you can handle runners. I'd say any dungeon would do. Just look at the rewards and work your points in the one that gives you the items you want in an achievable timeline.
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Wherever I go - there I am.