If you are trying to get more brain points to unlock better skills or abilities, you are going to need to level up. Every time you level up, you will earn a small amount of BP, and when you earn these points, you can use them to unlock various abilities in the game via the brain map.
But you will first need to earn these brain points by leveling up in the game, and you can level up by completing quests, progressing in the story, and slaying multiple others.
There's also the option of completing side quests in the game. You can get side quests after you complete the mission in the game that involves investigating a distress signal. Along with this, you will need to kill either Gunkin Perry or Dispen Perry before side quests unlock.
After this point, you will be able to find certain NPCs with diamonds over their heads that will indicate they have a side quest for you to accept.
That said, completing side quests and progressing and killing others in the game should allow you to level up with ease, and when you do level up you will get brain points.
Once you got brain points, you can then use them via the brain map in your inventory. You can find the brain map by pressing your inventory button and then finding the tab next to the equipment. From there, you will be able to get skills such as Rebound and attack boosts.
Check out all of our guides for Scarlet Nexus on PGG.