Do u have to be the alignment or can u just choose one the feat doesn't say ?

Your connection to an Outer Plane infuses you with the energy there. Choose a type of plane listed in the Planar Infusion Table. Your choice gives you a resistance to a damage type and the ability to cast a cantrip, as specified in the table. You can cast this cantrip without material components, and your spellcasting ability for it is Intelligence, Wisdom or Charisma (choose when you select this feat).

This is all it says.

Since it doesn't mention alignment (I don't have access to the book, so I'm relying on what you're saying), then alignment is irrelevant.

The feat lists no alignment-based restrictions, so you're free to choose which version you want for your character regardless of alignment.

I agree with the others. It just says a connection. Maybe you grew up near a portal to one of those outer planes, or you have an ancestor who is from one of them or something. 

But, as always, double check with your DM. They may rule otherwise. 

You should definitely check with your DM about whether this talent is allowed at all.  It is meant to be specific to Planescape campaigns so many DMs would not allow it.

Assuming the feat isn't banned by default, you're typically allowed to be any alignment but just have some RP connection to any one of the planes.  Much like Tieflings aren't required to be Lawful or to be Evil, even though they have a strong connection to the Nine Hells

Scion means both descendant and offshoot, sometimes for the purpose grafting when we're talking plant sciences.  The character is not the plane, or its alignment orientation, incarnate.  In fact, there's nothing prohibiting a character from being of a diametrically opposed alignment.

So RAW nothing is saying anything about force alignment.  Gameworld, that's a table's world building call, as Xalthu indicates. 

Thanks everyone 😁

The others covered this answer pretty well (i.e., no alignment restrictions unless the DM decides to institute them), but I was somewhat inspired with an idea based on the question and wanted to share a brief example of a character idea that would have differing feat/alignment traits...

Robert spent most of his youth and early adult life living in the gatetown of Automata. Both of his parents served as clerks and notaries for several of the higher-ranking officials within the lawful neutral town, and they oftentimes even took work orders from modrons and other denizens of Mechanus on the other side of the portal. Robert grew up learning all of the laws and rules that the local citizens were expected to know. Any remaining free time was spent behind a desk learning how to read and practice his calligraphy.

However, despite being saturated in lawfulness, Robert rankled during those long years. The most enjoyment he got was when he was able to illustrate a requested document, which usually got him scolded for being too gregarious in his style. Well, after years and years of being a squeaky cog in the machine, Robert final snapped and fled off into the surrounding Outlands. Robert now seeks a life of excitement and adventure. Most of all, he seeks freedom from the oppression that he felt so many years. Not just freedom for himself but for everybody who’s trapped within the bureaucracy.

Robert is a chaotic good human rogue, who has the Scion of the Outer Planes feat. Powers of Mechanus perfused him so thoroughly that he has the lawful version of the feat, but his desire to escape rigid bindings of law have led him to be chaotic in alignment.

Would need DM sign-off (as does any character concept), but I would expect that the above example would qualify under most reviews.

Quote from Rohun_the_wander >>

Do u have to be the alignment or can u just choose one the feat doesn't say ?

Your connection to an Outer Plane infuses you with the energy there. Choose a type of plane listed in the Planar Infusion Table. Your choice gives you a resistance to a damage type and the ability to cast a cantrip, as specified in the table. You can cast this cantrip without material components, and your spellcasting ability for it is Intelligence, Wisdom or Charisma (choose when you select this feat).

 

This is all it says.

"An Outer Plane".  The Outer Planes generally house same aligned beings.  In the spells section it tells you what cantrips you can use or damage you are resistant to basd the alignment of the Outer Plane you choose. 

"Connection to" is the operative part there; in terms of Planescape, there's the Outlands which connect to all of the Outer Planes, and at each connection there's a gate town inhabited by various individuals, usually including a variety of humanoids who ended up there for one reason or another. Living in a Gate Town is an easy justification for the feat.

Quote from The_Ace_of_Rogues >>

"Connection to" is the operative part there; in terms of Planescape, there's the Outlands which connect to all of the Outer Planes, and at each connection there's a gate town inhabited by various individuals, usually including a variety of humanoids who ended up there for one reason or another. Living in a Gate Town is an easy justification for the feat.

"Lived in a gatetown" is the suggested justification for the Gate Warden background, which grants the Scion of the Outer Planes feat, in fact.