Besides training, increases to your skills can come from two sources that stack: items and realm bonuses from earning realm ranks.

These increases to skills are capped as follows.

Items can increase a skill by a maximum of 1 + (your level/5) skill points.

Each realm rank (not realm level) beyond rank 1 increases all of your skills by +1.

Therefore you can earn up to 10 skill points by being rank 11. The total skill increase cap at level 50 is therefore 11 + 10 = +21 to a given skill.