Probably 50% of the 130+ skills are profession based, which means unless you are that profession you wont get some skills, other than that you could if you wish learn every skill that is learnable and raise them all … although the more skills you have that require time to raise the harder it is to keep them all maxxed simply because you gain xp from the skills like crafting so you find you level up faster
There are some skills like Gathering / Crafting and a few other misc. ones that can be bought from a trainer, everyone can buy them from the trainer so they are available to all.
Then there are class specific skills mainly these are Weapon/Magic skills you can not use a weapon or magic spell unless you know the class naturally from getting it from your profession … you can equip items to augment such skills but in the case of weapons and magic you need to know it naturally to use it.
So lets say I want to use swords but dont have sword skill, even if i got an item that raised my sword skill and equipped it I could not use swords simply because It did not come with my profession. On the other hand to complicate matters some skills that are class specific do work simply from items … skills like Taming/Tracking can be gained simply from using items however you cant “raise” the skill by using it, you are stuck at whatever value the item bonuses give and that limits you … where as someone who knows it naturally can raise it. Items have bonuses on them i.e. a piece of armor might have +ARMOR on it, it might also have +STAMINA when you equip the item you gain those bonuses.
Essentially any equippable item can have any STAT/SKILL on it as a bonus and you will find from time to time that as well as ordinary items that always have the same stats on them you will find unideitfied or magical items which may have random or different stats on them.
i.e. Rings … rings usually come with one random STAT or SKILL on them. So if you are smart you can collect rings that provide bonuses to special skills you dont naturally have like Beastmastery.