Leveling in Doggy Talents

Dogs gain levels by being fed treats, progressing through two stages: a normal track up to level 60 and a dire track up to a further level 30, for a maximum of 90.

During normal leveling the dog gains points and an extra 1 HP every other level, reaching a total of 27 HP at the end of the track. The dire track continues beyond that, adding more points and health each level until the dog reaches 30 HP at maximum dire level, at which point it also begins emitting nether-portal-style particles (configurable). Treats are tiered, and each can only raise a dog to a set ceiling:

At the top dire level the dog has reached its ultimate level and can no longer gain points. In current versions dogs are no longer permanently immortal and can die, but you can protect a dog by linking it to a Dog Bed: while the dog is standing, sneak-click the bed so the dog paths onto it and sits to become linked, after which right-clicking the bed revives a dead dog. With cheats enabled you can instead revive a dog by name with /dog revive byname <player> <dog name> (wrap the name in quotes if it contains spaces or special characters) or by its UUID with /dog revive byuuid <player> <dog uuid>.