Depending on the world you play you should have many chances to get most, if not all, of these achievements.
For the "Slayer of Phrodomo" and "Slayer of Chikhaton" you should deal ample damage during the boss fight with a team in each of their corresponding portals. Upon their deaths if you have done enough participation you will receive the achievement.
The "Teamplayer" achievement are also given in the mini-boss rooms upon entering the first time during the event.
The "Daring Trespasser" achievement is obtained by entering Devovorga's lair in Vengoth while the event is active.
The "Cocoon of Doom" achievement is obtained by dealing damage during the last minute of the fight with the Bloom of Doom. This achievement can be more difficult for a knight because standing next to it can literally kill you. Using distance runes such as avalanches, fireballs, etc along with exori hur can help you obtain this achievement.
The hardest achievement for anyone to get is the "Devovorga's Nemesis". This achievement is awarded to one or two (I know for fact one person will get it) players per event. The player(s) must have a lot of participation: dealing damage, receiving damage, healing, etc. This achievement will be difficult for any player, not just knights and will come down to luck and the number of participants present to kill Devovorga in her final stage.
In summary it is very possible to gain all of the achievements.
Just play it carefully for the "Cocoon of Doom" achievement and be very active in the final battle with Devovorga both in damage and blocking of the boss for the chance at obtaining "Devovorga's Nemesis".
