As skeletons have no organs to poison, they are immune to all poison damage, and the poisoned condition

Skeletons are resistant to necrotic  damage as they are already dead and that magic was used to make them

Skeletons are vulnerable to radiant magic as dark magic was used to reanimate it

Due to your eyesight being magical, with being able to see with no eyes and all. You can also see 60 feet through dim light as if it was bright light and darkness as if it was dim light. You can not discern color in darkness however, only shades of grey

Because of your odd condition, some things that don't affect the undead can affect you. Any beneficial spells which normally won't affect the undead that are used on you will work on you as if you are a human
You also have advantage on all saving throws that turn undead as you are an undead with free will

You have a significantly easier time removing your bones than other humanoid races. You can take a bone from your body and after taking 1d10 damage. You can use any bones you have as components for a spell, you can likely sell them, and you can even use it as a weapon if you have a free hand. There are many possibilities

Pick a humanoid race. You were a member of that race before you died, and you get the language that race had, along with its size, and its speed +5 (That extra speed is because you have no muscles or anything like that to weigh you down) and you look like the skeleton of that race. Your body is also vastly different than it was before so you do not get any other abilites, cantrips, resistances, or ability scores you get from that race

Your Dexterity increases by 2 and your constitution increases by 1. This is because you are faster now with your new body, with no skin, muscles, or anything like that weighing you down, increasing your dexterity and you have already died once, increasing your constitution

Skeletons can not age, however they rarely come up to the surface, especially being awakened so there isn't too much of them besides this

Skeletons tend to lean towards chaotic, as they are already dead and don't have much to care about. However this is not a guarantee, especially if their former race was lawful or neutral

Skeleton come from dead humanoids so their height is the same as the race they came from. For example with humans it would be medium or for halflings it would be small. They weight significantly less however due to being just bones

Your base walking speed is your former race's walking speed +5. You get extra speed since there is nothing to weigh you down

Due to formerly being a member of another race, you know common and a language your race speaks (for example if you were an elf, you speak elvish or a gnome, you speak gnomish) if you are a human, choose any language a human can. You can also speak Abyssal due to your time being dead and in the Abyss