player.skills

Player skills can be indexed by skill id or skill name.
Skills can also be indexed by skill category this will return a table containing the skills in the indexed category.
The table will be indexed by skill id.

Magic, Combat, Puppet Skills

great_sword = player.skills["Great Sword"]
print(great_sword.level, great_sword.capped)

Crafting Skills

goldsmithing = player.skills.Goldsmithing
print(goldsmithing.level, goldsmithing.capped, goldsmithing.rank_id)

Index by category

combat_skills = player.skills.Combat
for id, skill in pairs(combat_skills) do
    print("Combat Skill: ", id, skill.level, skill.capped)
end