I don't have Assasin nor know many things bout the class but it has been some time since this is posted maybe I could help Idk
On demand items that are easy to farm are harder to observe now, because only few people shout 'buy' in Rokoko. But based on popular classes today, you will probably find buyer faster if you farm their stuff.
Monk:
-☆Autoskill: Veltria (this one also drops quick use), Gewalt etc
-Dragon Mail◇: max it, refine to +9, up it and sell, many class need this
-Element xtal on add (almost all phys class need this): saw some Celawinos buyer but iirc Celawinos has barrier. Thotras is the most popular, monk will need the claw in near future.
Sniper:
-☆Quick Use: Raton (also drops Heinrich for Immo Sniper), Aldi etc.
-Ohirumeno: Shojo
Minstrel:
-☆Rate cut: Sword-Minenaga, Kaiser; Special-Raid 120; Add-Jahoel; Arm-Jabek
-Al crysta: Jahoel, Halios.
-◇Rudolf ◇Frederico
Not sure bout what alchemist needs nowadays but maybe something related to prod and their disable/resist gear..Some alch needs ◇Miasma
Assassin and glad population is rising too.
Common/Uncommon:
-Orichalcum. Everyone need this.
-MQ/SQ stuff. Put on stall and wait.
-Prod stuff.
Anniversary/Xmas interesting stuff:
-Halios
-Jahoel
-Vatendeth
-☆Quick Use from TIH
-Vida
-Warrior of Light
-BPC for oris, empty and chance for 2s
*Magic is dead.
-Rudolf
-Audlus (Freeze set for monk)
-Freesia weapon
-Toy Gloves◇◇
-Mistia
-Stoll&Buche (drop&xp mascot)
-Blue Rain
Don't forget to wear cake hat and get drop buff from santa to drop things easier
Hope this helps.