Pokemon Let's Go Awakening Value (AV) for all who level, or just the battle winner?
All Pokemon who level up gain AV values
As stated by Bulbapedia
At each level-up, a Pokémon will gain one AV on a random stat.
Awakening values
And Serebii
While each level you will get a random AV with each level up...
Pokémon Stats
Each Level up will give your Pokemon 1 random AV on any stat, it's just that the game will only show the stats growth from the Pokemon that is in battle, all other team members stats change are not shown like in previous games.