Pal Fluids are one of those items you'll need to get early on and aren't as intuitive to get as wood or rocks. Luckily, this resource is relatively easy to find very early on so you can stock up on it until the mid to late game.
Pal Fluids are generally found by knocking out water type Pals. The easiest way to find an abundance of water type Pals that will give you almost no trouble are the Pengullets on the Plateau of Beginnings. You do need to be aware that Pengullets will run away as soon as they see you, so make sure to be cautious and sneak up on them and hit them. The other option is to use a ranged weapon such as a bow. When provoked, they will use Ice Missiles to try to shoot at you, so make sure to pay attention to those and dodge them.
The map location of the Pengullets on the Plateau of Beginnings can be found here:
Once you have acquired some Pal Fluids, they can be used in making one of your first sanity structures in Palworld, the Hot Springs. These are essential for keeping your Pals happy while working. While Pengullets are great for getting these items, make sure to claim one or two of them for yourself since they make great workers at your base.