How can i level up after i reach 55hm 8

[Axx wolf]

I finish the main qusets

[Ludicium]

After this, the main method of leveling up is via experience charms, there's several types ranging from 10k, 100k, 1m and 5m (always transmute your exp charms). You can get these from the daily login.

Other methods which award exp are from daily quests, and killing mobs - however, the exp gained from these are so insignificant, you might say that the only method to level up is via exp charms.