So Unrelenting Skeptic is pretty neat! However it is found in the shadow tree which does not have Vigilance as a skill. Which seems very strange to me that it is a ability that uses a skill that the Shadow doesn't have. Any thoughts?

It has Well Rounded. I suppose if you want the Skill to be as cheap as possible. It and Cool would probably be good skills to grab with Well Rounded.

Well I do a agree those are good options I don't think a talent in a specialization tree should require a skill not included in that career or specialization just because Well Rounded is present. For example for the Character I would like to play I would rather have coordination and Lore (going for a Lora Croft Indiana Jones adventure feel). Personally I would take out Skulduggery and put in Vigilance. Which actually already fits well into the Shadow's theme.

Vigilance is a skill most people would put ranks in regardless though, isn't it?

I don't have my books in front of me, but I don't think it's uncommon for the spec trees to have one of the more interesting powers use a skill that isn't native to that spec. I presume that's to encourage players to spread their skills out instead of just maxing out the skills native to that spec.

If you're going for a Lara Croft-style feel, why not pick up Archaeologist? It has Knowledge (Lore) as a spec skill, and the talent tree helps give it the Lara Croft/Indiana Jones flavor.

Because the new game we are going to play is all force and destiny, our GM is super excited about it. No other material for now.

There's nothing preventing anyone from setting points into any skill they please. It just gets a tad more expensive if it's not a career skill. And even if you don't have the Vigilance skill you still have your Willpower characteristic.

And it's not too hard to pick up another specialization that does offer Vigilance as a bonus career skill.

Or if you're a Human, taking Vigilance as one of your bonus non-career skill ranks at character creation.

I am not saying that all isn't true. it just feels a bit odd being there in the middle of the tree and requiring a skill not found on the Shadow's list is all. If it was off as a lone side branch it wouldn't be too big of a deal. Maybe Trade it places with Shroud? I was just using my character as an example I am sure there are a lot of different skills a person would want for their Shadow without having to feel obligated to pick vigilance. Another talent in the tree I find odd is Anatomy Lessons for a specialization with no attack skills and is a barrier to the Force Rating talent. Maybe switch it out for some other talent or switch its place with Slippery Minded which makes more sense next to force rating in my opinion. Overall the Shadow specialization is really cool but sort of all over the place.

I see where that might seem odd. I suspect it's deliberate, though; throughout the spec trees you see things like this littered about. (stats or skills someone with this spec likely doesn't favor being important). As a quick example, take a look at Shien Expert: Shien Technique, the core of the whole thing, is built around using Cunning for Lightsaber and not needing Brawn. Yet the Falling Avalance allows them to add damage equal to Brawn. You see this in lots of other trees as well.

I suspect it's a deliberate attempt to encourage players to spread their skills and stats around. You'll see that to a lesser extent in some trees that encourage characters to take ranks in career skills they might not otherwise have invested in (the Sage's One with the Universe talent, for example, uses Astrogation).