A dog's damage in the game is determined by base values, passive perks, and equipment (collars).
It's important to understand that a collar ups your dog's damage to 20 points, but doesn't add this number to the existing basic attack (base damage is always 5 points, and the collar replaces the base damage for the value it indicates, which is 20 points, so in the end, damage with the collar becomes 20).

For example:
Without a collar or perks:
base damage is 5 points
Collar only:
20 (collar) + 0 = 20
Without a collar but with perks:
5 (base) + 15 ("Fighter" dog perk) = 20
With a collar and perks:
20 (collar) + 15 (if you have 3 dogs with the "Leader" perk) + 15 ("Fighter" dog perk) = 50

If you still have any questions, we're always happy to help!