How to get skill points quickly:
1. Unlock the waypoint 街道 - 骸骨洞窟
2. From the waypoint, keep going left to exit the level.
3. At the next level, keep advancing. Players will have to drop down a pit and fight a few enemies along the way (Skull pile, zombie, slime, zombie spearman, skull pile, zombie spearman, 2 skull piles)
4. After the final skull pile listed above, players need to jump up to proceed. At the second part where players have to jump, there will be two flying skulls and two skull piles. Keep proceeding left.
5. There'll be an intersection where players can choose where to proceed (jumping upwards). The left platform is the main path, has one zombie archer, one zombie spearman and one zombie swordsman.
6. The right intersection is where the juicy XP is. First time players enter there'll be a collectible orb at the end. This is where two Level 100 zombie swordsmen spawn as mini-bosses. Despite the level, they're just zombie swordsmen so they're easy to kill since their moveset is so predictable. THIS is where the XP comes in, since it's at least one level-up from just beating them.
Entire cycle stated above only takes 3-5 minutes to run, great for racking up the XP to earn skill points.
This is valid as of the latest Ci-En build, so mileage will vary as the game develops and the environments are adjusted. Other places to farm are full circuits of the town (with the serpent boss at the end) and the nameless hill side area recently introduced in the September 2022 build.