There are 4 or 5 trainers for each skill, total 40 trainers. Level limit is 40 which means you get 40 skill points from leveling and you have 4 skill points from racial bonus. You have 9 skills each with 10 points needed to master it -> you would need 90 skill points to master all skills. Let's confirm that by some math (warning for minor SPOILER): However, it seems it's correct that you can ask each trainer only once and the bug is that there is no message saying 'you already trained with this trainer'.
